Initial reports indicate there has been "no safety impact for nuclear power plants along the Pacific coast," the UN's nuclear watchdog says.

The International Atomic Energy Agency says it is in contact with Japanese national authorities about the earthquake and resulting tsunami.

Authorities were on high alert due to the earthquake, with workers at the Fukushima Daiichi and Fukushima Daini nuclear plant told to evacuate.

Image source, EPA/Russian Emergencies Ministry Handout

Authorities in Russia's far eastern Kamchatka Peninsula - near to where the powerful earthquake struck hours ago - have lifted tsunami warnings.

Posting on social media, external, Kamchatka's emergency minister says the "tsunami threat cancelled in Kamchatka".

Esme Stallard
Climate and science reporter

The Kamchatka Peninsula is remote but beneath the surface there is a lot happening.

Remember the earth's surface is split up into sections called plates. Just off its coast, the Pacific plate is moving northwest and coming into contact with another, smaller plate - called the Okhotsk microplate.

The Pacific plate is oceanic, which means it has dense rocks and wants to sink beneath the microplate.

As the Pacific plate sinks towards the centre of the earth, it is heating up and begins to melt - it effectively disappears.

But this process is not always smooth, often the plates can get stuck as they move past each other and the overriding plate is dragged downwards. This friction can then suddenly be released causing the plates to rebound.

This rebounding causes a megathrust earthquake.

The largest earthquakes every recorded in history, including Chile, Alaska and Sumatra which was responsible for the 2004 Boxing Day Tsunami, were all megathrust earthquakes.

This motion forces the ocean above it upwards, and displaces a large volume of water. This heightened part of the ocean then propagates outwards - this is the beginning of a tsunami.

Image source, BGS

Image source, EPA/Russian Emergencies Ministry Handout

The Russian government has given their first official reaction to the powerful earthquake, which struck in the far eastern part of the country.

Kremlin spokesperson Dmitry Peskov tells reporters that "all warning systems" had worked properly.

"Thank God, there were no casualties," he adds.

Shaimaa Khalil
Tokyo correspondent

Image source, Reuters

Thousands of people on Japan’s Pacific coast were woken up this morning by sirens alerting them to a tsunami.

Dozens of waves have hit Japan’s Pacific coast, with some more than a metre high, and officials say the risk is far from over.

In the searing heat - at the height of school holidays – families abandoned beaches with many stuck in traffic jams as they tried to move to higher ground.

The evacuation warning is a mid-level alert here, and spans hundreds of miles along the northern Pacific coast. But it has been downgraded to advisory levels throughout areas north of Tokyo to Wakayama prefecture in the south west.

The company which operates the Fukushima Daiichi nuclear powerplant - which suffered a meltdown in 2011 after a huge earthquake and tsunami - has said that all workers have been evacuated. There have been no abnormalities reported so far, the company says.

French Polynesian authorities have increased the maximum wave height prediction for the island of Nuku Hiva from 7.2ft (2.2m) to 13ft (4m).

The wave is expected any time after 01:00 local time (11:30 BST), authorities said. Nuku Hiva is the largest of the Marquesas Islands in the Pacific Ocean.

Other Marquesas Islands will be affected by wave heights between 0.6m and 0.9m, the latest statement adds.

Earlier, we heard that waves between 3.6ft (1.1m) and 7.2ft (2.2m) are expected for Ua Huka and Hiva Oa.

The tsunami waves are continuing to build along parts of the California coast as it begins to reach early morning, according to the National Weather Service Eureka.

There are tidal swings of up to 2.5ft (0.7m) within 15 minutes in San Francisco, the Bay Area weather service says.

"This can create some seriously dangerous currents along beaches and harbours. It's just a good idea to stay away from the water today!"

The maximum wave height recorded so far remains at 3.6ft (1.09m) in Crescent City, as we reported earlier.

Elsewhere in the US, waves are also being reported in La Push and Westport in Washington state.

Erwan Rivault
Senior data designer

Since modern seismography began in 1900, only five earthquakes have been stronger than the 8.8 magnitude earthquake off Russia’s coast. The most powerful on record remains the 1960 Valdivia earthquake in Chile.

The earthquake which hit near Russia's Kamchatka Peninsula is the most powerful to be recorded since the 2011 Great Tohoku earthquake in Japan, which triggered a devastating tsunami and led to the Fukushima Daiichi nuclear disaster.

A previous earthquake struck the same area near the Kamchatka Peninsula in 1952 with a magnitude of 9.

Mark Poynting
Climate and science reporter

At a provisional magnitude of 8.8, today’s earthquake ranks as one of the strongest ever recorded.

Here is the current list of the previous biggest ones, according to the US Geological Survey:

1. Biobío, Chile, 1960 – 9.5
2. Alaska, USA, 1964 – 9.2
3. Sumatra, Indonesia, 2004 – 9.1
4. Tōhoku, Japan, 2011 – 9.1
5. Kamchatka Krai, Russia, 1952 – 9.0

Before today, the next on the list were the 8.8-magnitude earthquakes off the coast of Chile in 2010 and Ecuador in 1906.

Image source, Reuters

Japan's Meteorological Agency has downgraded the tsunami warning level to "advisory" for coastlines from Kanto to Wakayama, but remains at the higher level of warning" for parts of Hokkaido and Tohoku.

Officials say tsunami are still being observed and there remains a risk of damage, adding that people in coastal areas should evacuate to safe places such as high ground or evacuation buildings.

Based on tsunami observation records from past earthquakes of nearly the same magnitude, authorities estimate that the high tsunami conditions will persist for at least a day.

Rozina Sini
BBC News

I’ve just spoken to Farrell Monaco in Makaha, Ohau in Hawaii who is on holiday from California, who says she was touring around the east coast when she initially noticed the tsunami advisory.

“People were still driving and kids were playing on the streets, so we didn’t bat an eye," she tells me.

“Then about 45 minutes later we hit traffic then the warnings started to come across and more news coverage.

“They were telling people in tsunami zones to move inland. That’s when everyone hit the roads.

“We foolishly thought we had time to get back to our vacation rental so we could pack up and leave - but then we hit traffic and realised we wouldn’t get back and then we ran out of gas."

Farrell describes a number of people lining up to get fuel; but reflecting on Hawaii downgrading the tsunami warning she said people did not panic.

“It was super nerve wracking waiting and waiting – you could hear a pin drop," she adds. “The disaster we were expecting did not come. They were so well prepared, they had air raid sirens and alerts.

“Everyone was on the roads and it was busy but it was all very civilised."

A tsunami warning has been issued for the Marquesas Islands in French Polynesia, with local authorities warning waves between 3.6ft (1.1m) and 7.2ft (2.2m) are expected in the coming hours.

The waves are expected to hit the islands of Ua Huka, Nuku Hiva, and Hiva Oa, authorities say, urging people in the area to evacuate to high-rise or refuge areas.

There is no need for evacuation for the rest of French Polynesia, though people are urged to avoid coastlines, beaches and river mouths.

News of tsunami alerts and advisories across the Pacific are flooding in. Let's take a minute to go over what exactly these warnings mean.

The US National Weather Service has a four-tier alert system for tsunamis.

Warning: Dangerous coastal flooding and powerful currents possible, move to high ground or inland.

Advisory: Strong currents and waves dangerous to those in or very near water possible, stay out of water, away from beaches and waterways.

Watch: Distant tsunami possible, stay alert and be prepared to act.

Information statement: No threat, very distant event or threat not determined.

The Philippines has cancelled its tsunami advisories put in place in several coastal communities.

The Department of Science and Technology says in an update that based on its data, no significant sea level disturbances or destructive tsunami waves have been recorded.

As we've been reporting, waves have reached the US west coast, where waves in Crescent City, northern California, have been recorded now at 3.6ft (1.09m), according to the National Tsunami Warning Center.

A warning remains in place from Cape Mendocino to the border with Oregon.

In Arena Cove, the waves have nearly doubled in height from 1.6ft (0.48m) to 3ft (0.9m) in the latest update.

Shaimaa Khalil
Tokyo correspondent

Image source, Reuters

The area affected by the tsunami across Japan is absolutely vast. We are currently at the mid-level of the country's alert system. But people are being told they need to watch what happens later in the day - the full impact will become clearer in a few hours' time.

The highest waves recorded so far have been 4.3ft (1.3m), and the authorities say they could reach as high as 9.8 ft (3m).

They also warn that when a tsunami coincides with high tide, the water could reach even higher - so people need to be careful even if the sea looks calm.

Residents in the affected areas have been told not to leave higher ground, and they are generally heeding the warnings. People have taken to rooftops on buildings in affected areas like Hokkaido. There is major disruption to train lines, and some flights have been cancelled.

Japan has experienced many earthquakes so the warning systems are very well-developed, and you constantly get updates on your phone.

We've also heard from the company which runs the Fukushima nuclear plant, which lies within one of the affected areas. Workers have been evacuated but the company was quick to say there have been no abnormalities.

Mark Poynting
Climate and science reporter

The outer layer of the Earth is divided into different sections called tectonic plates - a bit like the Earth’s puzzle pieces.

These plates move very slowly - perhaps only a few centimetres a year, which is roughly the same rate as your fingernails grow.

As they move against or towards each other, parts of the plates can get “stuck”, and stress builds up over a long period of time.

Eventually, this stress becomes too much and the plates jolt or slip back into place.

That releases the huge amounts of energy experienced in an earthquake.

If this occurs beneath the ocean, this movement can displace water in all directions, which can then travel to the coastline as a tsunami.

We can bring you an update from the US state of California now, after we reported that waves had reached the shore there.

The first measurements from the National Tsunami Warning Center show a wave of 1.6ft (0.48m) hitting Arena Cove, where the tsunami first reached California.

In Monterey, where we also know the tsunami waves are hitting, a height of 1.4ft (0.42m) was recorded.

In Port San Luis, the Los Angeles weather service says there's a "rapid and damaging surge, going from low to high tide in just a few minutes". People are asked to avoid the area.

Waves have also arrived in San Francisco, the National Weather Service reports.

In Canada, wave heights have so far remained below 1ft (0.3m), with the highest at 0.9ft in Winter Harbour, British Columbia.

Residents in Chocó and Nariño on the east coast of Colombia have been told to evacuate beaches and coastal areas, the country's National Unit for Disaster Risk Management says.

The agency says to move away from the coast to higher ground.

Image source, Geophysical Survey Of The Russian Academy Of Sciences Handout

We are tracking the latest developments as the tsunami threat continues to ripple across the Pacific Ocean - let's bring you up to date with what we know so far:

• A powerful 8.8 magnitude earthquake hit eastern Russia - about 78 miles (126km) from Petropavlovsk-Kamchatsky
• The tremor - which had a depth of 18km according to the US Geological Survey - is one of the strongest earthquakes ever on record
• There are no reports of any injuries or fatalities, but photos from towns and areas around the far eastern coast of Russia show buildings destroyed, ports submerged and people being evacuated by officials
• Waves generated by the tsunami have started to hit American shores along Hawaii's islands and off the coast of northern California
• Hawaiian officials have downgraded tsunami alerts to an advisory level, and told residents that they may return home with caution
• Western US states - including Washington, Oregon and Alaska - as well as Canada's British Columbia are on alert with waves expected to hit in the coming hours; warnings of varied levels have also been issued for Ecuador, Indonesia, Peru, Colombia and Japan
• Nearly 2 million people in Japan have been ordered to evacuate in parts of the country
• Initial waves reaching Japan have been much smaller, but its meteorological agency says they could grow to 3m (9.8ft)