In the last hour, we brought you the latest figures from Turkey, where officials say at least 3,381 people have died after the quakes.

Now we've got the latest estimates from Syria. More than 1,500 people are thought to have died there, both in government and rebel-held areas.

The political situation in Syria makes it trickier for official counts like this to be done. The search and aid operation is also thought to be much bigger in Turkey.

These latest figures come from rescuers themselves and Syrian state news agencies. Again, the number is likely to keep changing, stick with us for the latest updates.

Quentin Sommerville
Reporting from Adana, southern Turkey

Image source, Getty Images

The heavy machinery worked through the night here in Adana, klieg lights illuminating the collapsed buildings and huge slabs of concrete in monochromatic scenes repeated across southern Turkey.

Occasionally the work would stop, a call of Allahu akbar would rise up when a survivor is found, and too when the dead were recovered.

A big Turkish and international rescue effort is under way here. My plane from Lebanon was full of firefighters and paramedics, on arrival Adana airport was packed with Swiss and Romanian rescue workers in their hundreds.

The city is full of the homeless. Those who lost their homes and others too fearful of aftershocks to return to apartments and houses. The first earthquake struck in the middle of the night, 03:20 local time (00:20 GMT). It shook and thundered for 90 seconds, it felt like forever, but at the same time was only an instant to collect belongings and leave for safety. Some left without shoes, coats and phone chargers. Temperatures are expected to drop below freezing later this week.

Image source, .

As much as this is a catastrophe for Turkey, the situation in northern Syria is more desperate. The border remains tightly controlled, there is no international rescue effort and little heavy machinery.

The 1.7 million displaced people living on the border thought their lives couldn't get any worse, then the earthquake came. They'd been living in temporary shelters and half-finished buildings for years, refugees in their own country, escaping Syrian President Bashar Al Assad's reign of terror.

In Jinderes, Aleppo, and Bsania, Idlib, entire towns collapsed around the people. They call out for help and cry in pain, but there is almost no one to respond to their calls. In northern Syria more than a decade of war left the people had almost nothing, this terrible earthquake has left them with even less.

Image source, EPA

We've just heard from David Wightwick, of UK-Med, who's waiting to board a flight to Turkey where he'll lead the UK's medical response team there.

He says the initial crew of six people includes surgeons, paramedics, emergency medical staff and logistics staff. More NHS staff will likely join them, he tells Radio 4's Today programme, but it's important for them to arrive first and see how they can best help.

They don't want to take up too much space before they know what it is they can do to assist Turkish officials, he says.

Asked what it's like arriving in a disaster zone, Wightwick says it's "unsurprisingly chaotic, for fairly obvious reasons". He says teams like his usually face a litany of logistical barriers, such as closed roads.

"I've worked cross-border before in Turkey," Wightwick tells the BBC, referring to the damage in Syria, "the infrastructure was good then... whether that's still the case remains to be seen."

Simon King
Weather presenter and meteorologist

After heavy rain and significant snow in southern Turkey and northern Syria, it will generally get drier and sunnier through this week.

Some snow showers are still possible on Tuesday but with colder air digging in, freezing conditions will cause even more concern.

In Gaziantep, where the first quake struck, it will be around 4-6C by day - but plummeting overnight to -7C. It could be as low as -15C in the towns and villages towards the mountains.

It won't be as cold in Syria, but no more than 10 or 11C by day and -3C by night.

As we've been reporting, many people are having to huddle around makeshift fires on the street, too afraid to go home for fear of another deadly tremor.

Image source, .

The latest figures are here. In Turkey, the number of people who've died because of these earthquakes has risen to 3,381, according to the country's disaster authority.

Orhan Tatar, an official at the Disaster and Emergency Management Authority (AFAD), says a further 20,426 have been injured and 5,775 buildings collapsed.

The new count brings the combined death toll in Turkey and neighbouring Syria to 4,890.

This number is likely to keep rising, stay with us for all the latest developments.

Image source, EPA

In its latest update, Turkey's disaster and emergencies agency AFAD says 2,660 personnel from 65 countries have been sent to help in the search and rescue operation.

Together with the Turkish rescuers, 13,740 people have already been assigned to work in the disaster area. They are using 629 cranes and 360 vehicles.

The AFAD also says an air bridge has been established, and 146 aid-delivering sorties have already been made.

In total, 300,000 blankets and 41,504 family tents have been delivered, along with heaters and kitchen sets.

India has sent search and rescue teams and relief supplies to earthquake-hit Turkey.

Indian Foreign Ministry Spokesperson Arindam Bagchi said Delhi had sent its first batch of teams with medical supplies, trained dog squads, drilling machines and other necessary equipment to the nation.

He tweeted photographs of supplies being loaded on to an Indian air force plane, which took off from Delhi early Tuesday morning.

On Monday, Prime Minister Narendra Modi said that “sympathies of 1.4 billion people of India are with the earthquake-affected people of Turkey".

Turkish Ambassador to India Firat Sunel has expressed his gratitude, saying that "a friend in need is a friend indeed".

Image source, Reuters

If you're just joining us - here's the latest from Turkey and Syria:

• It's now just after 08:45 local time there, and a massive search and rescue operation that continued overnight is expected to pick up speed
• The confirmed death toll has surged to more than 4,300 - but it's likely to rise further as more sites are searched in the wide area
• Turkey's emergency agency AFAD says more than 2,600 personnel from 65 countries have been sent to the disaster area to assist Turkish rescuers
• In total, 300,000 blankets and more than 41,00 family tents have been delivered
• Thousands of buildings have collapsed after the 7.8 magnitude quake near Gaziantep, Turkey, hit in the early hours of Monday while people were asleep
• A 7.5-magnitude tremor then hit nearby several hours later, causing further damage to a region that was already badly shaken

Stay with us for all the latest updates from our correspondents on the ground, eyewitness accounts and experts' analysis, as well as videos and photos from the disaster area.

Istanbul has dispatched about 13,000 rescue personnel to the earthquake zone early Tuesday morning, said Governor Ali Yerlikaya.

The team comprises staff and volunteers, and were sent particularly to the Hatay province.

Hatay has suffered devastating damage from Monday's earthquake - which also split the runway at Hatay Airport into two.

Rescuers are racing against the clock with several factors in their way now, a critical care expert said.

The lack of water and oxygen are critical barriers to survival, said Dr Richard Edward Moon of Duke University.

Each adult loses up to 1.2 litres of water daily.

"That's urine, exhale, water vapour and perspiration if there is any. At the point where eight or so litres has been lost, that's when a person becomes critically ill," said Dr Moon, who was speaking on BBC Newsday.

Furthermore, it is winter now in Turkey and Syria.

An average adult can tolerate temperatures down to about 21C without the body losing its ability to maintain heat. But when it gets colder, it's a different story.

"At that point, the body temperature essentially follows the temperature of the environment. And the rate at which that may occur would depend on the insulation that the person may have, or how much shelter underground they may have. But ultimately, many of these unfortunate people may succumb to hypothermia," Dr Moon said.

"My heart goes out to those who are trapped, and also to the workers who are doing the best to get them out of trouble."

Aid planes from Iran and Iraq have arrived at Damascus International Airport.

The Iraqi planes carried about 70 tons of food, medical supplies and blankets, among other emergency supplies, Syrian state media SANA reported. These were delivered early Tuesday morning.

Iraqi's Prime Minister Mohammed Shia al-Sudani said on Monday they would send an aid shipment supplying first aid, shelter supplies, medicine and fuel.

Iranian aid arrived earlier on Monday. Iran's Foreign Minister Hossein Amirabdollahian had said on Monday that his country is ready to dispatch humanitarian aid to quake-hit areas in Syria.

Anna Foster
Reporting from Osmaniye, Turkey

As dawn breaks we’re heading for Maras, close to the epicentre of the quake and believed to be one of the worst-affected areas.

Traffic on the main highway is at a standstill, occasionally crawling forward, the wet road illuminated by glowing red brake lights.

Few people have made it to this part of southern Turkey yet, and everyone’s trying to get there as fast as they can to assess the damage and give vital help.

I just met a search and rescue team on their way to the city, their van loaded with specialist equipment and supplies.

They’re eager to get there and start looking for survivors, but they have no idea how bad the devastation will be when they arrive.

A new strong earthquake is now reported in central Turkey.

The US Geological Survey says a 5.5 magnitude tremor was at a depth of 10km (6 miles) near the town of Golbasi.

Meanwhile, the France-based European-Mediterranean Seismological Centre (EMSC) put the strength of the quake near Golbasi at 5.6, adding that it was at a depth of 2km.

Both agencies said the tremor happened at 03:13 GMT on Tuesday. They provided no further details.

South-eastern Turkey has been rocked by a series of aftershocks since the deadly earthquake near the city of Gaziantep on Monday morning.

Japan has sent a disaster relief rescue team to support search and rescue efforts in Turkey. The team departed for Turkey on Monday night.

Japan's Ministry of Foreign Affairs said in a press release on Monday, external: "Upon the request of the Government of Turkey, and in light of humanitarian perspective and Japan’s friendship relations with Turkey, Japan has decided to provide this emergency assistance to Turkey to meet its humanitarian needs."

Image source, Reuters

Red Crescent President Kerem Kınık warned people not to drive their cars to earthquake zones to donate relief supplies.

“Vehicles fell on 50m fault fracture on the roads. There is snow and ice on the roads," he said.

He asked people to instead donate food and supplies such as blankets, coats and boots to Red Crescent, which will distribute them, instead.

The group is also calling for blood donations, to help save the wounded.

Australian Prime Minister Anthony Albanese on Tuesday said his government would provide an "initial" 10m Australian dollars ($6.94m; £5.76m) in aid, to go to humanitarian groups.

"Australia's assistance will target those in greatest need," he said, expressing his condolences to those affected.

New Zealand's Prime Minister Chris Hipkins, who is visiting Australia, also announced his government would chip in 1.5m New Zealand dollars ($0.94m; £0.79m) in aid.

Image source, Getty Images

Pallab Ghosh
Science correspondent, BBC News

They are measured on a scale called the moment magnitude scale.

A tremor of 2.5 or less usually cannot be felt, but can be detected by instruments. Quakes of up to five are felt and cause minor damage.

The Turkish earthquake at 7.8 is classified as major and usually causes serious damage, as it has in this instance.

Anything above eight causes catastrophic damage and can totally destroy communities at its centre.

South Korea is the latest country to offer its assistance to Turkey.

On Tuesday morning, President Yoon Suk-yeol issued an order to send rescuers and emergency medical items to the country.

"Yoon ordered related government agencies... to come up with additional support measures in case needed by Turkey," a statement said.

Syrians gathered at a convent in Aleppo to spend the night as they feared more tremors following the deadly earthquake that hit on Monday.

One woman said she'd fled to the convent because it was in a remote area, free of tall buildings.

Image source, Getty Images

Freezing temperatures, snow and rain have hampered search efforts for survivors through the night in Turkey, as those trapped in the debris cry out for help.

One man in Hatay, a province in Turkey's south, wept in the rain as he described to Reuters the agonising wait for rescuers.

"They're making noises but nobody is coming," Deniz said, at times wringing his hands in despair.

"We're devastated. My God... They're calling out. They're saying, 'Save us,' but we can't save them.... There has been nobody since the morning."

Meanwhile, in Syria, Raed al-Saleh of the White Helmets - a rescue service in rebel-held territory - said they were in "a race against time to save the lives of those under the rubble".