A man with a knife has been seen within the confines of the Palace, eyewitnesses said.
Parliament has been placed on lockdown with MPs locked inside and armed police carrying shields protecting the building.
Reports suggest that 12 people have been injured and Scotland Yard said the attack is being treated as a “terrorist incident”.
A “police officer has been stabbed” and the “alleged assailant was shot by armed police”, Commons Leader David Lidington has told MPs.
Metropolitan police said they were called to a firearms incident on Westminster Bridge.
The Latest on reports of an incident outside Britain’s parliament (all times local):
The former Polish foreign minister Radoslaw Sikorski posted a video on Twitter that seems to show people lying injured in the road on Westminster Bridge.
Sikorski, a senior fellow at the Harvard Centre for European Studies, says he saw at least five people lying on the ground after being “mown down” by a car.
Sikorski told the BBC he “heard what I thought what I thought was just a collision and then I looked through the window of the taxi and someone down, obviously in great distress.
“Then I saw a second person down, and I started filming, then I saw three more people down, one of them bleeding profusely.”
London police say they are treating a gun and knife incident at Britain’s Parliament “as a terrorist incident until we know otherwise.”
The Metropolitan Police says in a statement that the incident is ongoing. It is urging people to stay away from the area.
Officials say a man with a knife attacked a police officer at Parliament and was shot by officers.
There are also reports of a vehicle hitting pedestrians on nearby Westminster Bridge.
A European security official says there was increased chatter on jihadi networks Tuesday following the UK’s adoption of an electronics ban aboard flights from certain mostly Muslim countries.
He said, however, there was no information that the incident was terror-related.
The official spoke on condition of anonymity because he was not authorized to speak about ongoing security operations.
—By Paisley Dodds.
The leader of Britain’s House of Commons says a man attacked a police officer at Parliament and has been shot by police.
David Lidington says the Parliament complex is in lockdown.
He says there are reports of further violent incidents neaby, and police say they have been called to a firearms incident on nearby Westminster Bridge.
Witnesses said a vehicle struck several people on the bridge, and photos showed a car plowed into railings.
The leader of Britain’s House of Commons says a man has been shot by police at Parliament. David Lidington also said there were “reports of further violent incidents in the vicinity.”
London’s police said officers had been called to a firearms incident on Westminster Bridge, near the parliament.
A session of Parliament was suspended after the incident.
Britain’s MI5 says it is too early to say if the incident is terror-related.