*Witnesses say car crashed into pedestrians
* Man shot after stabbing police officer
* Attack anniversary of Brussels killings
A policeman was stabbed, an assailant was shot and 20 people injured in what police said they were treating as a terrorist incident near Britain's parliament.
Four people have died in the incident Sky News said on Twitter, citing unspecified sources. Earlier it was reported that a woman had died and other people were being treated for "catastrophic" injuries after the attack in Westminster in London.
An image of the man believed to be the suspect has surfaced on Twitter:
Reuters reporters inside parliament heard loud bangs and shortly afterwards a Reuters photographer said he saw at least a dozen people injured on Westminster Bridge, next to the parliament, in what police said they are treating as a terrorist incident.
The House of Commons, which was in session at the time, was immediately suspended and lawmakers were asked to stay inside.
The leader of the House, David Lidington, said in the chamber that an assailant who stabbed a policeman had been shot by police. Officers - including firearms officers - remain on the scene and we are treating this as a terrorist incident until we know otherwise," London's Metropolitan Police said in a statement.
Prime Minister Theresa May was safe, a spokesman for her office said. He declined to say where May was when the attack took place.
On Twitter, Mayor of London, Sadiq Khan, issued a statement: “There has been a serious incident near to Parliament Square this afternoon which is being treated as a terrorist attack until the police know otherwise.
"I have spoken to the Acting Commissioner. The Metropolitan Police Service is dealing with the incident and an urgent investigation is underway. My thoughts are with those affected and their families.
Amid confusing scenes, it appeared the incident may have unfolded in several locations, including the busy bridge where tourists often congregate to take pictures of Big Ben and other attractions. The incident took place on the first anniversary of attacks on Brussels in Belgium."
The London Ambulance Service earlier said it had treated at least 10 people on Westminster Bridge. "We can confirm we have treated at least 10 patients on Westminster Bridge and have put a number of hospitals on alert as we continue to respond to this incident," said London Ambulance Service Deputy Director of Operations Pauline Cranmer in a statement.
Air ambulance is seen landing at Parliament Square, Westminster along with dozens of police cars:
London police said they were called to a firearms incident on Westminster Bridge near the British parliament on Wednesday.
Video posted on Twitter shows multiple wounded on the bridge:
Reporters inside parliament said a large number of armed police, some carrying shields, were pouring into the building. Britain is on its second-highest level of "severe" meaning an attack by militants is considered highly likely.
CAR "OUT OF CONTROL"
"I just saw a car go out of control and just go into pedestrians on the bridge," eyewitness Bernadette Kerrigan told Sky News. She was on a tour bus on the bridge at the time. "As we were going across the bridge, we saw people lying on the floor, they were obviously injured. I saw about 10 people maybe. And then the emergency services started to arrive. Everyone was just running everywhere."
Officials said an assailant had stabbed a policeman and then been shot. Witness reports suggested the assailant and the stabbed policeman were the people seen lying on the ground outside the parliamentary building. The House of Commons, which was in session at the time, was immediately suspended and lawmakers were asked to stay inside.
Journalist Quentin Letts of the Daily Mail newspaper told LBC radio that he had witnessed the stabbing of the policeman and the shooting of the assailant from his office in the parliament building. "He (the assailant) ran in through the open gates ... He set about one of the policemen with what looked like a stick," Letts said. "The policeman fell over on the ground and it was quite horrible to watch and then having done that, he disengaged and ran towards the House of Commons entrance used by MPs (members of parliament) and got about 20 yards or so when two plain-clothed guys with guns shot him."
US President Donald Trump told reporters at the White House he had been briefed on events in London but gave no details. The incident took place on the first anniversary of attacks on Brussels in Belgium.
Britain is on its second-highest alert level of "severe" meaning an attack by militants is considered highly likely. In May 2013, two British Islamists stabbed to death soldier Lee Rigby on a street in southeast London. In July 2005, four British Islamists killed 52 commuters and themselves in suicide bombings on the British capital's transport system in what was London's worst peacetime attack.
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
 "Westminster Bridge, UK Parliament, London, shooting, UK Parliament shooting, Theresa May, Big Ben")
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}
)
){kind=small}
){kind=small}
)
)
)
)
)
){kind=small}
){kind=small}
){kind=small}
){kind=small}
){kind=small}