A police officer has been stabbed in the Houses of Parliament in central London, in what police are treating as a terrorist incident.
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 crashing it into railings before running into the Palace of Westminster and stabbing the officer.
A Downing Street source said Prime Minister Theresa May was safe.
MPs said they had heard three or four gunshots.
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.
Staff inside Parliament were told to stay inside their offices.
Commons Leader David Lidington told MPs the “alleged assailant was shot by armed police”.
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.
“Armed police were quickly on the scene and I heard them shouting to people to get out of the yard.”