A British police officer was today stabbed in the Houses of Parliament in central London, in what police are treating as a "terrorist incident".
The incident prompted lockdown within the House of Commons chamber. Prime Minister Theresa May was seen being ushered into a car as what sounded like gunfire rang out at Parliament during the incident, the BBC reported.
Commons Leader David Lidington told MPs the "alleged assailant was shot by armed police".
There are also reports of as many as five people being "mowed down" on nearby Westminster Bridge.
MPs said they had heard three or four gunshots.
"Incident in #Westminster: We are treating this as a terrorist incident until we know otherwise," the Metropolitan Police tweeted.
"#Westminster: We thank the public for their assistance & urge people to remain calm, be alert & vigilant.
"Officers – including firearms officers - are on scene and dealing with the incident in #Westminster," it said.
Staff inside Parliament were told to stay inside their offices.
Press Association political editor Andrew Woodcock, who witnessed the scenes unfolding from his office window, said, "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," he said.
An eye witness, Radoslaw Sikorski, a senior fellow at Harvard's Centre for European Studies, posted a video to Twitter purporting to show 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.
Lidington said: "An air ambulance is currently attending the scene to remove the casualties.
"There are also reports of further violent incidents in the vicinity of the Palace of Westminster but I hope colleagues on all sides will appreciate that it'd be wrong of me to go into further details until we have confirmation from the police and from the House security authorities about what is going on."