LONDON — British police say five people died in the terror attack outside Parliament.
Counter-terrorism chief Mark Rowley said one policeman, three civilians and the attacker died.
He said a further 40 people were wounded.
The threat level for international terrorism in the U.K. was already listed at severe. Wednesday was the anniversary of suicide bombings in the Brussels airport and subway that killed 32 people, and the latest events echoed recent vehicle attacks in Berlin and Nice, France.
There was no immediate claim of responsibility and it was not clear if there was more than one attacker. London Police Commander B.J. Harrington said a full counter-terrorism investigation was underway.
A woman was confirmed dead. At least 10 people are being treated for injuries from the incident on the Westminster Bridge, according to a statement by the London Ambulance Service.
"There were people across the bridge. There were some with minor injuries, some catastrophic. Some had injuries they could walk away from or who have life-changing injuries," Colleen Anderson, of St. Thomas' Hospital, said.
The Metropolitan Police said in a statement that the incident is ongoing and urged people to stay away from the area.
The former Polish foreign minister Radoslaw Sikorski posted a video to Twitter that seems to show people lying injured on the span.
Sikorski, a senior fellow at the Harvard Centre for European Studies, said 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."
The Buckingham Palace gates have been closed as a precaution, according to the palace's press officer.
Facebook has initiated its "safety check" feature following the Westminster attack to allow users to mark they are safe near the incident.
Shortly after the attack was reported, NYPD's Counterterrorism Bureau said it is "monitoring" the situation in London. There is no known threat in New York City at this time.
A European security official said there was increased chatter on jihadi networks Tuesday following the UK's adoption of an electronics ban aboard flights from certain mostly Muslim countries.
The U.S. also adopted that ban, which temporarily bars passengers on certain flights from bringing laptops, iPads, cameras and most other electronics in carry-on luggage.
That security official 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.