A woman has died on Westminster Bridge in central London in what police are treating as a terrorist incident.

A police officer was also stabbed in the nearby Houses of Parliament by an attacker, who was shot by police.

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

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 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]."

Met Police Commander BJ Harrington said he was unable to confirm details of casualties.

Speaking outside Scotland Yard he said there was a "full counter-terrorism inquiry" under way.

He urged the public to stay away from the area around Westminster to allow emergency services access.

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.