One woman has died and a number of others have been hurt – including some with “catastrophic” injuries – in what police are treating as a terrorist incident in the Houses of Parliament in central London.

The attacker, who was shot by police officers, is reported to have earlier mowed down several pedestrians as he drove a car across Westminster Bridge.

He crashed it into railings before running into the Palace of Westminster and stabbing a police officer.

UK Prime Minister Theresa May was seen being ushered into a silver Jaguar car as what sounded like gunfire rang out at Parliament during the incident.

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

Leader of the House of Commons, David Lidington said that the “alleged assailant was shot by armed police”.

Describing the event, Press Association political editor, Andrew Woodcock, who witnessed the scenes from his office window said he 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.”

“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.

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

An eye witness, Radoslaw Sikorski, a senior fellow at Harvard’s Centre for European Studies, posted a video to Twitter showing people lying injured in the road on Westminster Bridge.

He wrote: “A car on Westminster Bridge has just mowed down at least 5 people.”

Transport for London said Westminster underground station has been shut at the police’s request, and buses diverted.