Eyewitness video shows five people 'mown down' by car on Westminster Bridge

"I heard what I thought what I thought was just a collision and then I looked through the window of the taxi and someone down, obviously in great distress," he told the BBC.

"Then I saw a second person down, and I started filming, then I saw three more people down, one of them bleeding profusely."

A car on Westminster Bridge has just mowed down at least 5 people. pic.twitter.com/tdCR9I0NgJ

— Radosław Sikorski (@sikorskiradek) March 22, 2017

A line of red buses and several ambulances could be seen on Westminster Bridge.

Alex Wafer, 47, who was cycling nearby and saw the aftermath, said: "At the end of the embankment it appears as though there is an ambulance.

"It looks as if they are treating somebody.

"And just below, it looks like there may be another paramedic treating someone else."

Kevin Schofield, the editor of PoliticsHome.com heard "a very loud bang" from the press gallery inside the Houses of Parliament followed by lots of shouting and men running around.

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He initially thought it was a car crash but then he looked outside the window to a heavily-guarded area outside which is out of bounds to the public.

He told Sky News: "Someone rushed through, attacked a policeman, a policeman went down, another policeman came and he was rescued.

"The man who had assaulted him got up and he appeared to be carrying either a knife or a gun. Then we heard gunfire, lots of gunfire, maybe five or six rounds.

"All I remember seeing is the man approaching the police officer probably with a knife and then there was gunfire.

"He was walking towards a second policeman with his arm outstretched, with what looked like a knife in his hand, having already assaulted another policeman.

"It was at that moment that you realised that something serious was happening - a man had broken in to Parliament and had a weapon."

Witness Quentin Letts said he saw a man in black attack a police officer outside Parliament before being shot two or three times as he tried to storm into 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 told the BBC.

"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."

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

He added: "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."

A man who did not want to be named said: "I just happened to be passing through Westminster Square.

"I heard shots and at about the same time saw a car that seemed to have mounted the pavement outside Parliament."

Eyewitness Rick Longley told the Press Association he saw a man stab a policeman.

Fighting back tears he said: "We were just walking up to the station and there was a loud bang and a guy, someone, crashed a car and took some pedestrians out.

"They were just laying there and then the whole crowd just surged around the corner by the gates just opposite Big Ben.

"A guy came past my right shoulder with a big knife and just started plunging it into the policeman.

"I have never seen anything like that. I just can't believe what I just saw."

Alan Parry, of Sky Sports News, was at Westminster for a meeting when he heard "an almighty crash" when he was just outside the underground station .

He could see what he thought was a 4x4 vehicle on the other side of the road which had crashed into some railings.

He told Sky News: "There was smoke coming this vehicle. I walked on a few paces further and saw what I assumed to be either a pedestrian or a cyclist who had clearly been hit and wasn't moving, although he did then gently move.

"The guy who I assumed was the driver of this 4x4 got out of the car and suddenly sprinted away from the scene - that was followed by four of what sounded much like gunshots.

"All of a sudden all hell was let loose. Police descended everywhere and the whole area was locked down."

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Steve Voake, 55, was walking across the Westminster Bridge towards the South Bank when he saw the aftermath.

He said he saw at least two bodies lying on the road and one in the water.

"I saw a trainer lying in the road and when I looked more closely I saw that there were a couple of bodies the other side of the road," he told the Press Association.

"And when I looked over the side there was another body lying in the water with blood all around it."

Watching the incident unfold from the press gallery inside the Houses of Parliament, George Eaton the political editor of the New Statesman told Sky News: "I saw a large crowd fleeing the attacker who appeared to be carrying a knife, fleeing him from close to the Tube station.

"He then entered the gates of Parliament and charged at officers. We now know that one of them was sadly stabbed. He was then very swiftly shot by armed police."

In the aftermath of the attack as Westminster was put on lockdown, he could see two ambulances inside the grounds of Parliament. He said that ministers have been evacuated and journalists have been ordered not to leave while nearby traffic has been stopped.

Tourist Kathy Casatelli, 58, saw a car rammed into the front gates of the palace and a man being treated on the floor.

She said: "We were coming up from the Tube and we walked out and there were officers there with their guns drawn.

"I saw this car that was smashed into the gate. It was grey ... it looked like a nice car. The whole windshield was smashed.

"There was a man on the ground, it looked like he was moving. I don't know if he was the driver."

Ms Casatelli, from Syracuse in the US and on holiday in London since Saturday, said she heard that someone had been wielding a knife.

She said: "One of the officers was trying to help him.

"He wasn't moving very much, I thought I saw him moving.

"I don't know if he was riding a bike and got hit. There was somebody with him and he was there with his hands on his head.

"I don't know if they were walking or biking and it hit them."

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Police extended the cordon back up Broad Sanctuary beyond Westminster Abbey to the junction with Victoria Street.

Four police vans arrived at the scene at 3.40pm, as the air ambulance took off.

Witness Richard Tice said he "counted between eight and 10 prostrate figures on the ground" after he came out of Westminster underground station and moved on to Westminster Bridge.

He told Sky News: "My understanding from someone who was standing next to me was that a car had driven along the whole pavement knocking people over and that is why there were many injuries. The people lying on the ground were starting to be attended to by a paramedic."

The London Eye tourist attraction, just across the Thames from Parliament, said it was on lockdown following the attack.

A spokesman said: "At present we are holding all of our guests within our attractions as per tried and tested security procedures."

Matt Haikin, from London, 44, said he was in shock after seeing the aftermath of the crash on the bridge.

He said: "I just saw a car that had clearly driven off the road into the fence outside Parliament.

"As I went past I noticed there was a body next to it and quite a lot of blood and people standing around.

"Fairly shortly after I heard some shots, at which point it was clear it wasn't just an accident, something else was going on."

He then moved to look through the Palace of Westminster gates and saw "a lot of people, people in uniform, I think I saw a couple of bodies on the ground, I couldn't tell you if they'd been asked to lie down or if they were injured".

Bradford Buck, from Connecticut in the US, saw the incident unfolding.

He said: "Police cars just kept coming one after another after another, I've never seen such a quick response. Then a little bit later the helicopter came.

"My wife and I came up from Westminster underground, we walked across to Parliament and there was a car crashed into the gate there.

"Police officers were running with machine guns, and there was a man down right next to the car."

Fearing for their safety, Mr Buck and his wife sheltered behind some concrete, before police moved them to safety.