Five people were killed and about 40 injured on Wednesday after a car plowed into pedestrians and a suspected Islamist-inspired attacker stabbed a policeman close to British Parliament.

A man driving a sport-utility vehicle ran over pedestrians on Westminster Bridge at around 2:40 pm. The driver then crashed into railings, got out of the car and attacked a policeman with a knife near the Palace Yard entrance to the House of Commons, before he was shot. The policeman, identified as Keith Palmer, 48, later died.

There were unconfirmed reports that police were hunting for a second man who may have accompanied the assailant in the vehicle. The assailant was given first aid and carried conscious to an ambulance.

Prime Minister Theresa May condemned the attack as "sick and depraved".

"The location of this attack was no accident," she said in a statement outside her 10 Downing Street office.

Mark Rowley, Britain's most senior counterterrorism officer, told reporters the investigation was working on the assumption that the attack was "Islamist-related terrorism".

Colleen Anderson, a doctor from St Thomas' Hospital, where the victims were being treated, confirmed that a female pedestrian had died after falling under the wheels of a bus. She told reporters: "I confirmed one fatality. A woman. She was under the wheel of a bus. She died. I confirmed her death at the scene."

She added: "There were people across the bridge. There were some with minor injuries, some catastrophic. Some had injuries they could walk away from or who have life-changing injuries. There were maybe a dozen people injured."

Officials confirmed a woman was rescued from the Thames River after apparently jumping from Westminster Bridge to escape the assailant's car.

The prime minister was escorted from the House of Commons by armed police minutes after the incident. Police also shut the gates of nearby Buckingham Palace, where Queen Elizabeth was in residence.

Several members of Parliament (MPs) and senior officials were caught up in the chaos. Tobias Ellwood, a junior Foreign Office minister, was pictured attempting to resuscitate a man believed to be the wounded policeman.

There were no reports of Chinese nationals injured in the attack. The Chinese embassy issued an alert to Chinese nationals visiting or staying in the UK, calling for raised vigilance and awareness, and urging them to avoid crowded areas.

May was scheduled to chair a meeting of the government emergency committee, also known as known as COBRA, to discuss the response to the incident.

The sitting of the House of Commons was suspended, and MPs were told to stay in the chamber. All other government buildings were "locked down". Police evacuated the House and other nearby buildings.

The Scottish Parliament in Edinburgh also suspended its debate on a second referendum on Scottish independence.

Witnesses described how the car plowed into pedestrians on Westminster Bridge before crashing into railings.

Bernard Cazeneuve, the French prime minister, confirmed that three French citizens, believed to be teenage schoolchildren, were injured in the car attack.

Quentin Letts, the Daily Mail's parliamentary sketchwriter, told the BBC he saw a man in black clothing attack a police officer before being shot two or three times as he tried to enter the House of Commons.

"I saw a thick-set man in black clothes come through the gates into New Palace Yard, just below Big Ben," he said. "He had something in his hand, it looked like a stick of some sort, and he was challenged by a couple of policemen in yellow jackets. And one of the yellow-jacketed policemen fell down, and we could see the man in black moving his arm in a way that suggested he was stabbing or striking the yellow-jacketed policeman.

'As this attacker was running towards the entrance, two plain-clothed guys with guns shouted at him what sounded like a warning; he ignored it, and they shot two or three times and he fell."

Angus McNeice and Bo Leung in London contributed to this story.

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