Four people have been killed, including a police officer, in a major terrorist incident just yards from the Houses of Parliament this afternoon.
Here's everything we know about the attack so far.
What happened in Westminster?
Around 2:40pm, an attacker mowed down about a dozen pedestrians on London's Westminster Bridge in a grey Hyundai i40 leaving one woman dead and others with "catastrophic injuries".
The vehicle then crashed into railings just yards from the Houses of Parliament and the attacker was seen running through the gates of the Palace of Westminster with a knife.
He reportedly stabbed a policeman before being shot "several times" by armed officers.
Paramedics fought to save his life and that of his victim on the floor of the cobbled courtyard just yards from the House of Commons. Two large knives could be seen at the scene.
How many casualties are there?
Four people are confirmed dead, including a police officer. At least 20 people have been seriously injured.
A female pedestrian died after being hit by the attacker's car on Westminster Bridge and was confirmed dead by a doctor at St Thomas' Hospital.
Details of the other victims are still emerging.
Three French teenagers on a school visit to London were among those injured at the bridge.
Le Telegramme reported the students, aged between 15 and 16, were wounded in the attack with one ending up on the roof of the car. The pupils from a school in Concarneau, Brittany, had arrived in London on Sunday evening.
Another woman who apparently jumped into the Thames as the attacker drove across the bridge was rescued and given urgent medical treatment on a nearby pier.
Is it a terror attack?
Scotland Yard has declared the attack a terrorist incident and said a counter-terrorism investigation is already under way.
What do we know about the suspect?
No details are yet known.
Where is the Prime Minister?
Prime Minister Theresa May was seen being ushered into a silver Jaguar in the grounds of the Palace of Westminster. A Downing Street source confirmed she was "OK".
She is currently monitoring the situation from Downing Street and will chair a meeting of the Government's emergency Cobra committee later today.
Parliament has been suspended.
Are roads closed?
Police are asking the public to avoid the following areas this evening: Parliament Square, Whitehall, Westminster Bridge, Lambeth Bridge, Victoria Street up to the junction with Broadway and Victoria Embankment up to Embankment Tube station.
Officers also want anyone with images or film of the incident to hand those to the police.
Is London safe?
Scotland Yard is appealing for the public to remain vigilant and say public safety is their number one priority. Extra police will be deployed across the capital.
Facebook has activated its Safety Check feature. People in the area can use the tool to mark themselves as "safe" which will be visible to their friends on the network, as well as to see if friends nearby have done the same.
