UK Parliament locked down after apparent terrorist incident

An injured person is assisted after an incident on Westminster Bridge in London, Britain March 22, 2017.  [Photo/Agencies]

Radosław Sikorski, a Polish politician, told the BBC he saw four people on the ground on the bridge.

"I didn't see a car, but I heard what I thought was a collision," he said. "I looked through the window of the taxi and I saw someone down, obviously in great distress."

Amine Morada, from Algeria, was in Parliament Square when the incident happened: "I heard a loud bang, bang. I looked around and saw a man on the ground with blood coming out of his head. He was white with black hair and was wearing backpack. People were screaming. It was chaos. I saw a crashed car and two people were slumped on it. It had smoke coming out of it and water coming out the bottom. I thought it was an accident."

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 apparently 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.

"The other officer ran to get help and the man in black ran about 15 yards towards the entrance.

"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 contributed to the story