A police officer was one of those killed.
One woman was pulled alive from the River Thames amid chaos in the area, the heart of political life in Britain. The assailant also died.
Parliament was placed on lockdown and lawmakers were forced to remain in the main debating chamber of the House of Commons as fireamrs responded to the incident outside.
The Mayor of London, Sadiq Khan, said the incident was “being treated as a terrorist attack until the police know otherwise.”
Pictures showed scenes of carnage in the aftermath of the attack, which happened as parliament was in session. One member of the British government gave mouth-to-mouth resuscitation to one of those injured.
One woman is confirmed to have died during the incident. Officer stabbed, assailant appears to have been shot, House leader says. Large section of central London in lockdown. Gates to Buckingham Palace closed. Social media video shows bodies on Westminster bridge. Car crashed into Parliament perimeter fence. Witnesses describe pedestrians mowed down by car.
Incident began near Westminster Bridge
London’s Metropolitan Police said on Twitter they were called at approximately 2:40 pm to reports of a firearms Proceedings in the House of Commons were suspended with dozens of MPs locked inside.
Images emerged of a car crashed into the perimeter gate of Parliament, and witnesses later told CNN that they saw the vehicle mow down pedestrians.
Police soon put the Westminster area on lockdown, securing roads, Parliament buildings and the Westminster underground station. But that zone soon expanded to a larger part of central London.
The London Eye, popular with tourists, was among areas in lockdown.
Mayor of London Sadiq Khan said: “There has been a serious incident near to Parliament Square this afternoon which is being treated as a terrorist attack until the police know otherwise.
“I have spoken to the Acting Commissioner. The Metropolitan Police Service is dealing with the incident and an urgent investigation is underway. My thoughts are with those affected and their families.
“I would like to express my thanks to the police and emergency services who work so hard to keep us safe and show tremendous bravery in exceptionally difficult circumstances.
Police said in a statement that a full response unit had been sent to the scene, along with ambulance crews and air ambulances.
“We have declared a major incident and our priority is to assess patients and ensure that they are treated and taken to hospital as soon as possible.”
Police appealed for anyone with photos or video of the incident to pass them on to police.
Commander BJ Harrington said “There are a number of casualties including police officers.”
Parliament on lockdown
Leader of the House, David Lidington, told MPs in session that a serious incident had taken place “within the estate.”
“It seems that a police officer has been stabbed, that the alleged assailant was shot by armed police,” he said.
“An air ambulance is currently attending the scene to remove the casualties. There are also reports of further violent incidents in the vicinity of the Palace of Westminster but I hope colleagues on all sides will appreciate that it’d be wrong of me to go into further details here until we have confirmation from the police and from the House security authorities about what is going on.”
Members of parliament were asked to keep away from windows.
They were later due to be evacuated in groups of 20, MP Simon Danczuk told CNN by telephone from inside.
Around half an hour after the attack, former Cabinet minister Anna Soubry said on Twitter she and Security Minister Ben Wallace were ordered into the Parliament lobby at gun point by police.
“Colleagues taken out of the library at gun point by counter terrorist armed police officers,” she tweeted.
Parliament was in the middle of a vote when the incident occurred, MP Sir Gerald Howarth said the House of Commons said. “It appears to be very, very serious indeed,” he said.
“The Leader of the House has told us it’s been confirmed that one police officer here has been stabbed. It appeared that a car was coming towards the House of Commons mowing down pedestrians on the way and the driver then got access to the parliamentary estate stabbed a police officer and was shot.”
Eyewitnesses report chaotic scenes
People were photographed running in a panic from the scene.
An eyewitness told CNN that he heard a car collision at Westminster Bridge and saw at least five people on the ground.
“I heard — rather than saw — what I took to be a collision, like a car hitting a sheet of metal, and then I looked again and I saw people down on the streets, on the tarmac,” witness Radek Sikorski told CNN by phone.
“I saw in all, five people down by a car, including one person bleeding heavily from the head, and another person lying unconscious.”
“I saw them seconds after impact, but there’s also a hospital right there by Westminster Bridge.”
Richard Poet, 62, who was visiting London from Brighton and his partner were leaving the Tate Britain gallery when he heard “great crashes.”
“I thought it was a wrecking ball. It didn’t sound like guns or anything.”
Craig Meichan, 20, a student from Ormskirk near Liverpool, was on a field trip with around 15 others and had left Parliament just a moment before. He was shaking as he told CNN his part was separated into three groups.
“It sounded like a car backfiring, police began shouting and they started cordoning off the area,” he said, adding that he believed his tutor was still locked inside.
“I’m a bit shaken up, you never expect this to happen to you. When it does it’s an indescribable feeling.”
US President Donald Trump at a Women in healthcare panel told reporters he was getting updates from London.
“Some big news having to do with London just happened,” he said.
Mark Toner, acting spokesperson for the US State Department. said officials were closely following the situation.
“Our hearts go out to those affected. We stand ready to assist in any way the UK authorities would find helpful,” he said.
Member of Parliament gives assistance
A member of the government, Foreign Office Minister Tobias Ellwood, was pictured giving assistance to a victim in New Palace Yard, a courtyard within the grounds of Parliament,
A fellow Conservative Party MP, Maria Miller said he had “given mouth-to-mouth resuscitation to one victim,” the Press Association said.
Eyewitness Hugh Dickinson, a 21-year-old student from High Wycombe, posted a picture of the minister on Twitter, showing the minister bleeding, but saying “he looked to be fine”, the Press Association said.
By Angela Dewan, CNN