UPDATE: Scotland Yard said Wednesday afternoon that four people died and at least 20 were injured. The dead include the police officer who was stabbed and the attacker who was shot by an officer. Police said there was one attacker, but the investigation is continuing into the terrorist incident. 

Eyewitnesses described the horrifying scene on Westminster Bridge, where an attacker ran over people before stabbing a policeman outside the U.K. Parliament. 

Police said they're treating the attack as a "terrorist incident" at this juncture and at least two people were killed, with several more injured. The U.K. Parliament remains on lockdown. 

The leader of the House of Commons David Liddington confirmed the suspect was shot by police.

More than 10 pedestrians and cyclists were reportedly mowed down by the SUV before it smashed into the gates surrounding parliament.

A student told Sky News he had just left to walk to a nearby university when someone ran up to him and said "there's been a terrorist attack on the bridge."

He said he ran to the scene and saw about 3-4 people who'd clearly been struck by the vehicle.

A second eyewitness said he was on the bridge when the attack unfolded. He said a bus suddenly stopped and he heard people screaming.

He said he saw two bodies on the bridge and another in the water of the River Thames below.

He said he immediately ran toward the bridge entrance to stop more people from coming onto the bridge. The man described a 5-10 minute "lull" before emergency responders arrived.

Another man told Sky News he saw the attacker stab the police officer.

"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," he said.

Watch the witness accounts above and below. Read more on the attack, here.

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