Four dead, including police officer, 20 injured in UK parliament attack

Scene outside UK parliament where four people were killed in a suspected terror attack. 

At least a dozen people were injured and four reported dead in London on Wednesday after a car crashed into pedestrians near the British parliament and an assailant stabbed a policeman in what police called a terrorist incident.

The knifeman was then shot by police in the shadow of Big Ben, where he had tried to force his way into a courtyard just outside the Houses of Parliament.

"Four people have died. That includes the police officer who was protecting parliament and one man we believe to be the attacker who was shot by a police firearms officer," Britain's top counter-terrorism officer Mark Rowley told reporters.

The incident appeared to have unfolded in several locations, including on nearby Westminster Bridge where eyewitnesses said a car had crashed into pedestrians.

Reuters reporters inside parliament heard loud bangs and shortly afterwards saw two people lying on the ground in a courtyard just outside.

A Reuters photographer said he saw at least a dozen people injured on the bridge. His photographs showed people lying on the ground, some of them bleeding heavily and one under a bus.

Sky News reported two people had died, but the total number of casualties was unclear. The London Ambulance Service said it had treated at least 10 people on the bridge.

The incident took place on the first anniversary of attacks by Islamist militants that killed 32 people in Brussels.

"Officers - including firearms officers - remain on the scene and we are treating this as a terrorist incident until we know otherwise," police said in a statement.

"We know there are a number of casualties including police officers but at this stage we cannot confirm numbers or the nature of these injuries," Commander BJ Harrington told reporters.

"We received a number of different reports which included a person in the river, a car in collision with pedestrians and a man armed with a knife."

A woman was pulled alive, but with serious injuries, from the Thames, the Port of London Authority said.

French Prime Minister Bernard Cazeneuve said three French nationals were injured. French media reported they were high-school students.

Car "out of control"

"I just saw a car go out of control and just go into pedestrians on the bridge," eyewitness Bernadette Kerrigan told Sky News. She was on a tour bus on the bridge at the time.

"As we were going across the bridge, we saw people lying on the floor, they were obviously injured. I saw about 10 people maybe. And then the emergency services started to arrive. Everyone was just running everywhere."