Updated March 23, 2017 19:19:03

Photo: Armed police worked to move people on as they locked down the area around the British Parliament in London. (Reuters: Stefan Wermuth)

Central London was plunged into chaos as a driver ran down pedestrians on Westminster Bridge before entering the grounds of the Houses of Parliament and stabbing a policeman to death.

Four people died in the attack, including the assailant, and at least 40 were injured, including an Australian permanent resident who lives in South Australia.

This is how events unfolded.

Warning: This story contains graphic images.

Witnesses described how a car accelerated from the southern end of Westminster Bridge around 2:40pm local time and sped towards the Houses of Parliament and Big Ben.

Among those hit as the car mounted the pavement were a group of French schoolchildren and three policemen returning from an award ceremony.

At least one person was seen falling from the bridge into the River Thames. The BBC reported she was later pulled from the river and taken to hospital.

Photo: A man lies bleeding on the pavement after the attack (Reuters: Toby Melville)

The car sped past Big Ben and crashed into railings outside Parliament as police scrambled to the scene.

Photo: The car mounted the footpath and smashed into railings, before the driver abandoned it to enter the Parliament's grounds. (AP: Yui Mok)

Photo: Heavily armed police officers scramble to secure the area. (Reuters: Stefan Wermuth)

The driver pulled out a knife, climbed out of the car and entered the grounds of the Houses of Parliament.

A policeman who confronted him was stabbed in the struggle and later died of his injuries.

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

The attacker was shot dead as armed police moved in.

Photo: London police surround a man on the ground, with an armed officer pointing a gun at him. (AP: Stefan Rousseau)

Photo: The attacker lies on a stretcher, while being treated by paramedics as police look on. (AP: Stefan Rousseau)

MP rushes to help dying man

Conservative MP Tobias Ellwood saw the stabbed policeman lying on the ground and tried to give him mouth to mouth resuscitation.

"I tried to stem the flow of blood and give mouth to mouth while waiting for the medics to arrive but I think he had lost too much blood," he told reporters afterwards.

Photo: Conservative MP Tobias Ellwood was the first to rush to the officer's aid. (AP: Stefan Rousseau)

Photo: Tobias Ellwood, his forehead smeared with blood, stands and looks concerned after helping the stabbed officer. (AP: Stefan Rousseau)

Air ambulance flies in amid scenes of panic

With people fleeing in panic, the Houses of Parliament in lockdown, and bystanders taking refuge in nearby Westminster Abbey, an air ambulance flew in to treat the injured.

Photo: An air ambulance lands in London's Parliament Square shortly after the attack on Westminster Bridge. (Reuters: Stefan Wermuth)

Photo: Heavily-armed police crouch beside a hedge as they secure the area outside London's Houses of Parliament. (AP: Stefan Rousseau)

Topics: terrorism, england, united-kingdom

First posted March 23, 2017 10:48:14