Four people, including a police officer and the lone attacker, have died in a terror attack near the Houses of Parliament in London.
Two of those killed were among more than 20 pedestrians hit by a car on Westminster Bridge, before it crashed.
The man stabbed the officer outside Parliament before being shot dead.
PM Theresa May said it was a “sick and depraved” attack on the heart of the capital and attempts to defeat UK values were “doomed to failure”.
Speaking in Downing Street after chairing a meeting of the government’s Cobra emergencies committee, Mrs May paid tribute to the “exceptional men and women” of the police force who responded to the attack.
“We will all move forward together, never giving in to terror and never allowing the voices of hate and evil to drive us apart,” she said.
The prime minister added: “The location of this attack was no accident. The terrorist chose to strike at the heart of our capital city where people of all nationalities, religions and cultures come together to celebrate the values of liberty, democracy and freedom of speech.”
The attacker has not yet been identified.
Acting Deputy Commissioner and head of counter terrorism at the Metropolitan Police, Mark Rowley, said a major investigation was under way into the “marauding terrorist attack”.
He said emergency services were called at 14.40 GMT after the car was driven over Westminster Bridge, hitting and injuring a number of members of the public and three police officers, who were on their way back from a commendation ceremony.
After the car crashed into the railings of the Houses of Parliament, a man armed with a knife “continued the attack” and tried to enter the building.
Eyewitnesses said police fired three or four gunshots as the knifeman lunged towards a second officer.
Foreign Office minister Tobias Ellwood – a former Army officer whose brother died in the Bali terrorist bombing in 2002 – attempted mouth-to-mouth resuscitation of an injured police officer.
The officer who was killed was said by Mr Rowley to have been armed – but police later confirmed that was not the case.
In latest developments:
- The prime minister said the UK terror threat level would remain at severe – its second highest – meaning an attack is “highly likely”
- Westminster underground station was shut and remains open for interchange only
- Home Secretary Amber Rudd urged everyone to remain calm but be vigilant and if they see anything they are concerned about report it to the police
- A group of French schoolchildren were on the bridge and three were injured
- 13 students from Edge Hill University in Lancashire were also caught up in the incident – two were taken to hospital and described as walking wounded; two others had minor injuries
- There are two police casualty bureau numbers: 0800 056 0944 and 0207 158 0010 for people worried about family and friends, or eyewitnesses
- Kings College Hospital says eight patients are being treated there – six male, and two female. Two are critical and two are stable
- St Thomas’ Hospital said two patients had been admitted – both are stable
- The Port of London Authority said a woman was pulled alive from the River Thames near the bridge and was being treated for serious injuries
By Dominic Casciani, home affairs correspondent
The incident outside Westminster is exactly the kind of scenario that security chiefs have been planning for.
It looks like the type of attack jihadis have wanted to carry out in Britain – namely attacking people with a vehicle and taking on the security forces with knives.
In the security services’ jargon this is known as a “marauding attack” and is the hardest type of terrorist incident to predict and defend against. That means casualties, as we have seen in Nice and elsewhere, are inevitable.
But what matters just as much is how the police then respond.
Armed police at Parliament were able to stop the attacker. Within minutes, Westminster was flooded with more armed officers, including counter-terrorism specialists.
Inside Scotland Yard, teams of detectives began working on the next critical phase – establishing the suspect’s movements, whether he acted alone and, in tandem with their colleagues on the street, making sure London is as secure as it can be in light of these awful events.
Westminster remains locked down and it will remain so until Scotland Yard is certain the threat has been contained.
‘Screams and commotion’
Press Association political editor Andrew Woodcock witnessed the scenes unfolding from his office window overlooking New Palace Yard.
“I heard shouts and screams from outside and looked out, and there was a group of maybe 40 or 50 people running round the corner from Bridge Street into Parliament Square.
“They appeared to be running away from something.”
“As the group arrived at the Carriage Gates, where policemen are posted at the security entrance, a man suddenly ran out of the crowd and into the yard.”
An eye witness, Radoslaw Sikorski, a senior fellow at Harvard’s Centre for European Studies, posted a video to Twitter showing people lying injured in the road on Westminster Bridge.
- As Parliament was put into lockdown, MPs said they were told to stay inside their offices.
- Around 1,000 people were taken to Westminster Abbey for safety and were then being processed by police
- MPs were locked in the House of Commons for more than four hours and business suspended
- The House of Commons and Lords will sit at their usual times on Thursday
- Over the following days there will be extra unarmed and armed officers on the streets of London
- The White House said Mrs May had spoken to President Donald Trump about the attack
- Paris mayor Anne Hidalgo says the Eiffel tower will go dark at midnight in homage to the London victims
- London mayor Sadiq Khan praised citizens and emergency services for their “tremendous bravery” and said: “Londoners will never be cowed by terrorism.”
Metropolitan Police Federation chairman Ken Marsh said: “We offer our deepest sympathy to the family of the officer who has died. This incident shows the dangers our colleagues face on a daily basis.”
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