A policeman has been stabbed and his attacker shot by officers after a major terrorist incident at the Houses of Parliament.

The attacker mowed down several pedestrians as he drove a 4x4 across Westminster Bridge before crashing it into railings then running through the gates of the Palace of Westminster and stabbing the officer.

Eyewitnesses said he was shot by police as he approached a second officer clutching his knife.

He left a trail of destruction as paramedics tended to his victims on the bridge and at the gate.

Prime Minister Theresa May was seen being ushered into a silver Jaguar in the grounds of the palace as what sounded like gunfire rang out at around 2.45pm.

A Downing Street source confirmed she was "OK".

Eyewitness Rick Longley described the attack:

"We were just walking up to the station and there was a loud bang and a guy, someone, crashed a car and took some pedestrians out. Rick Longley, eyewitness

Around three shots rang out as the attacker ran through the gates into the front yard of the parliamentary compound.

Two people - thought to be the knifeman and the officer - were then seen being treated on the ground in New Palace Yard amid shouts and screams.

An air ambulance landed in Parliament Square and a regular ambulance came in through the front gates as medics rushed to help the injured people.