At least 12 people were reported injured in a stabbing and car ramming outside the British parliament in London and on the nearby Westminster Bridge.

The parliament was on lockdown after an assailant stabbed an officer, then was shot dead by police, officials said. London Police also said officers were called to an incident on Westminster Bridge nearby.

Police said they were treating the attack “as a terrorist incident until we know otherwise.” They said in a statement that the incident was ongoing and urged people to stay away from the area.

It was not immediately clear exactly what happened or how many people were injured. On the bridge, witnesses said, a vehicle struck several people, and photos showed a car plowed into railings. Witnesses in Parliament reported hearing sounds like gunfire.

London's air ambulance arrives at the Houses of Parliament in central London on March 22, 2017 during an emergency incident (AFP PHOTO / DANIEL LEAL-OLIVAS)

London’s air ambulance arrives at the Houses of Parliament in central London on March 22, 2017 during an emergency incident (AFP PHOTO / DANIEL LEAL-OLIVAS)

Witness Rick Longley told the Press Association news agency that he saw a man stab a policeman outside Parliament.

“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,” he said. “They were just laying there and then the whole crowd just surged around the corner by the gates just opposite Big Ben. A guy came past my right shoulder with a big knife and just started plunging it into the policeman.

“I have never seen anything like that. I just can’t believe what I just saw.”

Lawmaker Adam Holloway told the AP he saw people running and immediately ran into his offices in Parliament to be with his staff. “A lot of us are locked in with our staff at the moment,” he said.

A police officer stops traffic as the Jaguar car of British Prime Minister Theresa May (R) is driven away from the Houses of Parliament in central London on March 22, 2017 during an emergency incident. (AFP PHOTO / Daniel LEAL-OLIVAS)

A police officer stops traffic as the Jaguar car of British Prime Minister Theresa May (R) is driven away from the Houses of Parliament in central London on March 22, 2017 during an emergency incident. (AFP PHOTO / Daniel LEAL-OLIVAS)

David Lidington, the leader of parliament’s lower House of Commons who is responsible for arranging government business, told MPs: “What I am able to say to the house is there has been a serious incident.

“It seems that a police officer has been stabbed, that the alleged assailant was shot by armed police. There are also reports of further violent incidents in the vicinity of the Palace of Westminster,” he said.

He said he could not go into further details until there was confirmation from the police and security authorities.

Prime Minister Theresa May is safe, a statement from her Downing Street office said, and she was seen getting into a car and being driven away from parliament.

Lidington said a helicopter was at the scene to take away casualties.

Video from Westminster Bridge showed apparent casualties moments after the attack.

British lawmaker Grant Shapps said on Twitter that he was walking through the cloisters of the House of Commons to vote when he heard four gunshots. Police told lawmakers to get down on the ground and crawl to cover.

“Police response instant. Heard commotion, looked round. Police weapons drawn, 4 shots, police ordered us to hit ground & get back, get back,” he said.

Journalists there said they were told to stay in their offices. The Press Association reported that two people were seen lying within the grounds of Parliament.

George Eaton, a journalist with the New Statesman, said that from the window of Parliament’s Press Gallery, he saw police shoot a man who charged at officers.

“A large crowd was seen fleeing the man before he entered the parliamentary estate,” he wrote on the publication’s website. “After several officers evaded him he was swiftly shot by armed police.”

A staff member in parliament, who did not want to be named, told AFP: “I definitely heard shots. I saw someone in dark clothing go down.”

Passengers evacuating the Brussels Airport, in Zaventem, after a string of explosions rocked Brussels airport and a city metro station, March 22, 2016. (AFP Photo/Belga/Dirk Waem/Belgium OUT)

Passengers evacuating the Brussels Airport, in Zaventem, after a string of explosions rocked Brussels airport and a city metro station, March 22, 2016. (AFP Photo/Belga/Dirk Waem/Belgium OUT)

The incident came on the same day that Belgium was marking a year since its most deadly attack, when 32 people were killed in suicide bombings at Brussels Airport and a metro station.

In July 2005, four British suicide bombers inspired by Al-Qaeda attacked London’s transport system during rush hour, killing 52 people.

Two weeks later, there was an attempt to carry out a second wave of attacks.