LONDON, United Kingdom (AFP) —British police shot a suspected attacker outside the Houses of Parliament in London on Wednesday after an officer was stabbed in what was described as a “terrorist” incident.

According to witness reports, a car also ploughed into several bystanders on the nearby Westminster Bridge before crashing into railings outside parliament.

The building in the heart of the British capital was immediately sealed off and MPs and staff ordered to remain inside.

“We are treating this as a terrorist incident until we know otherwise,” police said in a statement.

The incident comes with Europe on high alert after a series of deadly jihadist attacks.

Belgium was on Wednesday marking a year since its most deadly attack, when 32 people were killed in suicide bombings at Brussels Airport and a metro station by Islamic State fighters.

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

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.

One eyewitness, Jayne Wilkinson, told Press Association she had seen the drama unfold.

“We were taking photos of Big Ben and we saw all the people running towards us, and then there was an Asian guy in about his 40s carrying a knife about seven or eight inches long.

“And then there were three shots fired, and then we crossed the road and looked over. The man was on the floor with blood.

“He had a lightweight jacket on, dark trousers and a shirt.

“He was running through those gates, towards Parliament, and the police were chasing him.”

US President Donald Trump said he had been briefed on the incident, describing it as “big news.”

A Downing Street source said Prime Minister Theresa May was “okay” but declined to say where she had been during the attack.

She had earlier been in parliament during her weekly showpiece question and answer session.

She was seen getting into the back of a car and being driven off.

The incident came a day after Britain announced it planned to follow the United States and introduce a ban on electronic devices in cabins on flights from some Middle Eastern and North African countries.

Affected airlines have until Saturday to implement the measure.

US officials warned that terrorists are seeking “innovative” ways to attack airliners with smaller explosive devices hidden in consumer electronics larger than smartphones.

Lidington said an air ambulance was at the scene outside parliament to take away casualties.

TV pictures showed traffic halted on the nearby Westminster Bridge and emergency vehicles swarming around. The busy bridge was completely shut off to traffic.

Armed police rushed to the area which was quickly sealed off to the public.

London’s Metropolitan Police said on Twitter: “We were called at approx 2:40 pm to reports of an incident at Westminster Bridge. Being treated as a firearms incident — police on the scene.

“Officers — including firearms officers — are on scene and dealing with the incident.”

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.”

Westminster station on the London Underground train network, which is opposite the Houses of Parliament, was closed over to the incident.

The Houses of Parliament, designed by Charles Barry and Augustus Pugin, were completed in 1870 and are now a UNESCO World Heritage Site.

The site is heavily guarded around the clock and there are barriers designed to prevent someone ramming into the building.

On Saturday, a man who had been investigated for links to radical Islam was shot dead at Paris’s Orly airport after attacking a soldier on patrol and grabbing her rifle.