Metropolitan Police Chief Cressida Dick said two stabbing victims had died and three injured people were being treated in a hospital

A man wearing a fake explosive vest stabbed several people on Friday in London, killing two in what police are treating as a terrorist attack, before being tackled by members of the public and then fatally shot by officers on London Bridge, officials said.

Metropolitan Police Chief Cressida Dick said two stabbing victims had died and three injured people were being treated in a hospital.

She said police were working “at full tilt” to determine whether anyone else was involved in the attack.

The violence erupted two-and-a-half years after a van and knife attack in the same area killed eight people, and less than two weeks before Britain holds a national election. The main pollical parties temporarily suspended campaigning in London as a mark of respect.

Prime Minister Boris Johnson said that “to the best of our knowledge, the incident has been contained” but that details were still emerging.

Mr. Johnson’s office said the prime minister would chair a meeting of the government’s emergency committee, COBRA, later on Friday evening.

Metropolitan Police counterterrorism chief Neil Basu said the suspect appeared to be wearing a bomb vest but it turned out to be “a hoax explosive device".

Mr. Basu said officers were keeping “an open mind as to any motive.”

Ms. Dick, the police chief, said officers were called just before 2 p.m. to Fishmongers’ Hall, a conference venue at the north end of London Bridge. The pedestrian and vehicle bridge links the city’s business district with the south bank of the River Thames, was reported about 2 p.m.

Cambridge-based prison-education organization Learning Together was holding an event there on Friday, and the University of Cambridge said it was “gravely concerned” about students, staff and alumni who might have been caught up in the attack.

Minutes after the stabbings report, witnesses saw a knifeman being wrestled to the ground by members of the public on the bridge before armed-response officers shot him dead.

One video posted on social media showed two men struggling on the bridge before police pulled a man in civilian clothes off a black-clad man on the ground. Gunshots followed. Another depicted a man in suit and overcoat holding a long knife that apparently had been taken from the attacker.

Other images showed police, guns drawn, pointing at a figure on the ground in the distance.

Karen Bosch, who was on a bus crossing the bridge, said she saw police “wrestling with one tall, bearded man” and then heard “gunshots, two loud pops.”

She said the man “pulled his coat back which showed that he had some sort of vest underneath, whether it’s a stab vest, or some sort of explosive vest, the police then really quickly moved backwards, away.”

Another bus passenger, Amanda Hunter, told the BBC that the vehicle “all of a sudden stopped and there was commotion and I looked out the window and I just saw these three police officers going over to a man.”

“It seemed like there was something in his hand, I’m not 100% sure, but then one of the police officers shot him.”

Police confirmed that the man died at the scene.

The mayor Sadiq Khan praised the “breathtaking heroism of members of the public who literally ran towards danger not knowing what confronted him.”

"They are the best of us,” Mr. Khan said.

The prime minister also praised the bystanders, and said anyone who was involved in the attack “will be hunted down and will be brought to justice.”

Cars and buses on the busy bridge were at a standstill after the shooting, with a white truck stopped diagonally across the lanes. Video footage showed police pointing guns at the truck before moving to check its container.

London Bridge station, one of the city’s busiest rail hubs, was closed for several hours after the attack.

Scores of police, some armed with submachine guns, flooded the area, ushering office workers and tourists out of the area, which is packed with office buildings, banks, restaurants and bars. Staff in nearby office blocks were told to stay inside.

As police cleared the streets, staff in shops and restaurants ushered customers into storerooms and basements. Some had been through similar traumatic events- In June 2017, eight people died in a van and knife attack in the same area.

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In that attack, three assailants inspired by the Islamic State group ran down people on the bridge, killing two, before stabbing several people to death in nearby Borough Market.

The 2017 fatal attack took place days before a general election. Britons are due to go to the polls again on Dec. 12.

Political leaders expressed shock and sorrow at Friday’s attack.

"We will not be cowed by those who threaten us,” Labour Party leader Jeremy Corbyn said. “We must and we will stand together to reject hatred and division.”

Both Labour and the Conservatives suspended campaigning in the city after the attack and the prime minister was also canceling political events for Saturday.

Another bridge in London was the target of attack in March 2017, when an attacker killed four people with a car on Westminster Bridge then fatally stabbed a police officer before security forces shot and killed him in a courtyard outside Parliament.

Security officials earlier this month downgraded Britain’s terrorism threat level from “severe” to “substantial,” which means an attack is seen as “likely” rather than “highly likely.” The assessment was made by the Joint Terrorism Analysis Centre, an independent expert body that evaluates intelligence, terrorist capability and intentions.

The U.K.’s terror threat was last listed as “substantial” in August 2014; since then it has held steady at “severe,” briefly rising to “critical” in May and September 2017.