The scene of the shooting in London outside the House of Commons

A police officer who stabbed in a terror attack at the Houses of Parliament by an attacker died at the scene from knife injuries.

It is understood a police colleague who tried to keep him alive with mouth-to-mouth first aid told paramedics he was already dead following the brutal stabbing.

The attacker struck several pedestrians as he drove a car across Westminster Bridge, before crashing it into railings.

A woman injured in the attack also died from her inuries.

A doctor at St Thomas’ Hospital said a number of other people were hurt – some with “catastrophic” injuries.

Junior doctor Colleen Anderson from St Thomas’ said she also said she treated a police officer in his 30s with a head injury, who had been taken to King’s College Hospital.

She said the woman had died at the scene.

“There were people across the bridge. There were some with minor injuries, some catastrophic,” she added.

“Some had injuries they could walk away from or who have life-changing injuries. There were maybe a dozen [injured].”

MPs said they had heard three or four gunshots and staff inside Parliament were told to stay inside their offices.

Commons Leader David Lidington told MPs the “alleged assailant was shot by armed police”.

A Downing Street source said Prime Minister Theresa May was safe.

The prime minister was seen being ushered into a silver Jaguar car as what sounded like gunfire rang out at Parliament during the incident.

She is to hold a crisis COBRA security meeting this evening with police and intelligence to review London’s security.

Tom Peck, political editor for the Independent, tweeted: “There was a loud bang. Screams. Commotion. Then the sound of gunshots. Armed police everywhere.”

Press Association political editor Andrew Woodcock witnessed the scenes unfolding from his office window overlooking New Palace Yard.

“I heard shouts and screams from outside and looked out, and there was a group of maybe 40 or 50 people running round the corner from Bridge Street into Parliament Square.

“They appeared to be running away from something.

“As the group arrived at the Carriage Gates, where policemen are posted at the security entrance, a man suddenly ran out of the crowd and into the yard.

“He seemed to be holding up a long kitchen knife.

“I heard what sounded like shots – I think about three of them – and then the next thing I knew there were two people lying on the ground and others running to help them.

Scene on Westminster Bridge after several people reported injured after shooting

“Armed police were quickly on the scene and I heard them shouting to people to get out of the yard.”

Scotland Yard’s anti-terrorist squad is now investigating the incident.