People are being evacuated from the scene of the attack.

Image source, AFP

Image source, AFP

Image source, Reuters

And there are more pictures from the attack here.

Kenya's police boss Joseph Boinnet has just finished a press briefing about the attack at the DusitD2 hotel in the capital, Nairobi.

He said armed assailants attacked the hotel and are still inside the building.

Security officers are now in the building and people are being screened and evacuated, Mr Boinnet said.

He added that some people had been injured but that officials were assessing them.

Kenya police chief Joseph Boinnet has called the events at a Nairobi hotel a "suspected terror attack":

A BBC reporter at the scene of the attack says he can hear gunfire three hours after the incident began.

Bile Beshir Mehbub is a journalist at Radio Tusmo in Nairobi. He is in Westlands, near the scene of the attack.

Daniel Kulecho has emailed the BBC to say he left work early to collect his daughter from school and that traffic in Nairobi was unbelievable.

"I left work quickly to pick my daughter to safety from school, about 1km away from Dusit. Traffic is unbelievable! Our office safety team has organised a WhatsApp roll call for people to respond with SAFE."

He told the BBC he was OK; "we are so scared though," he added.

The Somalia-based militant group al-Shabab has said that it is responsible for the attack.

On one of its media outlets it has given details about how the attack was carried out.

It says it started with a big explosion and was quickly followed by the forced entry of armed men into the "targeted" hotel.

Today's attack comes three years to the day after al-Shabab militants attacked a Kenyan military base in Somalia where nearly 200 soldiers were killed.

Read more:What happened when al-Shabab attacked a Kenyan base in Somalia?

People have been fleeing the scene of the attack in Westlands escorted by heavily armed soldiers; one man has been led out with a gunshot wound in the back.

One office worker explained what had happened to her:

Tuesday's attack is the latest in a series of attacks in Kenya that have been claimed by the Somalia-based group al-Shabab.

• In 2013 al-Shabab militants killed at least 67 people in an attack on a shopping complex, the Westgate Mall
• In 2015, at least 147 students died in an attack on a university campus in Garissa

Kenya's main TV stations are providing live coverage of the aftermath of the attack on the hotel in the Westlands suburb of Nairobi:

People are being evacuated from the Dusit hotel complex after two explosions and gunfire were heard:

The BBC's Ferdinand Omondi has sent us these pictures of the security forces at the scene of the attack in Nairobi:

Photos show the scene of the attack on the Dusit hotel complex in Kenya's capital, Narobi, where security forces are evacuating the buildings and moving people to safety:

Image source, Reuters

Image source, Reuters

Image source, Reuters

Image source, Reuters

In a call to the BBC, a spokesman for Somalia-based militant group al-Shabab has claimed responsibility for what he said is "an on-going operation in Nairobi".

The spokesman did not give details of the operation, but said al-Shabab will give further details once it is over.

Here's what we know so far about the attack on a hotel complex in the Westlands area of Nairobi:

• Reports say at least two explosions were heard, followed by sustained gunfire.
• Police say for now they are treating it as a terrorist attack.
• People have been leaving the scene escorted by heavily armed soldiers; one man has been led out with a gunshot wound in the back.
• Medics are at the scene and the head of Kenya's Directorate of Criminal Investigation is leading rescue efforts.
• The surrounding buildings are being evacuated and the area has been cordoned off.

A Kenyan journalist at the scene of the attack reports that witnesses say armed men arrived at the hotel complex and entered Dusit hotel, in the Westland district of the city, before they started shooting.

The head of Kenya's Directorate of Criminal investigations, George Kinoti, has arrived at the scene of the attack in Nairobi's Westlands neighbourhood:

The BBC's Ferdinand Omondi reports that Mr Kinoti is there to lead the team in rescuing those trapped inside.

Medics are at the scene, tending to people who have been injured in the attack.

The BBC's Ferdinand Omondi reports that witnesses say they saw four armed men entering a complex which houses a hotel in Kenya's capital, Nairobi.

He has tweeted that an armed security officer has told him "things are not good".

A witness has been sharing videos of the explosion in Kenya's capital, Nairobi.

In one, people can be seen running away as the sound of gunshots ring around the area.