Armed men mowed down several pedestrians on London Bridge late Saturday before being shot dead by police, killing at least seven in what officials described as an act of terror, Britain's third major attack in as many months.

Police flooded London streets after a van jumped the road and struck dozens of civilians, then headed to nearby Borough Market, a commercial area filled with bars and restaurants. They left the vehicle and stabbed people in those establishments before being shot down by security forces.

The London police reported that three attackers, wearing fake explosive vests, were shot dead by armed response officers and believe that there were no more attackers than those killed. London Ambulance told Reuters that 48 injured people were sent to hospitals across London into early Sunday morning in the UK, several of them in critical condition.

"We are treating this as a terrorist incident and a full investigation is already underway, led by the Met's Counter Terrorism Command," Metropolitan Police Assistant Commissioner Mark Rowley said in a statement.

"We are reviewing and planning to strengthen our policing stance across London over the forthcoming days, and there will be additional police and officers deployed across the Capital," Rowley added.

He said that the van struck people on London Bridge around 10:00 p.m. local time on Saturday and continued to Borough Market where a number of people were stabbed by the assailants, including an on-duty British Transport Police officer who responded to the incident at London Bridge.

The three assailants were "confronted and shot by the police within eight minutes of the first call," Rowley said, adding that what looked like explosive vests on the attackers turned out to be "hoaxes."

London Metropolitan Police Chief Cressida Dick later told reporters on Sunday that the death toll now stood at seven confirmed dead, adding the the area of the attack is now cordoned off and everyone advised to stay inside until police get in touch.

The London Bridge overground and underground stations will remain closed and he repeated that police presence in the city will be heavy in key areas, Dick said, adding the identity of the attackers remains unknown.

Our "understanding" is that 3 people were involved, Dick told a press conference, but that "we must make sure there isn't."

Britain's counter-terrorism command is leading the investigation into the attacks, the police were quoted as saying earlier.

Britain is still reeling from a terror attack at a Manchester concert that left dozens dead and put the country on a high state of alert ahead of Parliamentary elections next week. British Prime Minister Theresa May called an urgent security meeting and was joined by London Mayor Sadiq Khan in condemning the attacks.

Khan later added that the terrorism threat level remains at "severe" - meaning an

attack is highly likely - and said that the police presence in the city will be increased from Sunday.

Khan on Twitter.

Saturday's attack comes just days ahead of a June 8 U.K. parliamentary election that has tightened unexpectedly in recent days. While May is expected to keep her majority, several polls have suggested her Conservative Party has slowly surrendered a once commanding lead.

A new attack, coming on the heels of the Manchester bombing, could once again shake up the political terrain.

On Sunday, the Conservatives, Labour and the Scottish National parties among others agreed to suspend national campaigning for the day, according to Reuters, though some local campaigning will continue. But the UK Independence Party said it would refuse to stop campaigning because "disrupting our democracy is what the extremists want."