London Bridge was evacuated Saturday night after a van crossed a curb and plowed into crowds and at least three terrorists exited and went on a stabbing rampage.
At least seven victims are feared dead and 48 injured. Three attackers have been killed by police, the U.K.'s Sun reported.
The incident was part of a series of coordinated terror attacks in two different areas of the city. A third stabbing incident, which occurred at the same time, is being viewed as unrelated by police.
Police swarmed the popular tourist and entertainment area, telling people to leave and take shelter, even dragging diners out of restaurants for their own safety, reported the Sun.
One terrified woman described police firing weapons. "We had to run. There was loads of shooting," she said.
Another witness said: "There's been about eight of them stabbed. I ran up to see if they were all right but people were already with them. I was bloody terrified.
"I thought, is that real? If we had of been on the other side of the road, it could have been us."
Reuters reported a witness said she saw three victims with wounds that looked as though their throats had been cut.
A statement issued from 10 Downing Street said, "The prime minister is in contact with officials and is being regularly updated on the incident at London Bridge."
President Trump was briefed on the incident and tweeted: "We need to be smart, vigilant and tough. We need the courts to give us back our rights. We need the Travel Ban as an extra level of safety!"
He followed with a second tweet minutes later: "Whatever the United States can do to help out in London and the U.K., we will be there – WE ARE WITH YOU. GOD BLESS!"
A second incident occurring at nearby Borough Market, where police responded to a stabbing and shots were fired.
From witness descriptions, the attackers were men who had jumped from the van after it ran down pedestrians. A witness, named only as Andrew, told LNC Radio he saw them running toward the bars and restaurants in Borough Market, wielding large knives.
"There was a guy with a big knife - I mean, I mean, a big knife," he said. "I hid behind a little bush for probably 10 seconds, maybe 20 seconds. Then I ran for my life."
Another eyewitness told the BBC that the men who jumped from the van were stabbing people indiscriminately, shouting, "This is for Allah."
"They literally just started kicking them, punching them, they took out knives. It was a rampage really," he said.
"They headed down towards Southwark Cathedral towards the bar, and starting running at people.
"People at the bar started fighting back. Then the three of them decided to make their way up to the bridge
"A woman was staring at them, and they started stabbing her.
"Throughout the whole way across the bridge, there were people littered across bleeding. People were trying to help each other."
Witnesses described two or three men armed with 12-inch long knives who were stabbing pedestrians. Others describe the weapons as machetes.
While at Borough Market, two attackers entered a restaurant and stabbed two victims inside, reported Fox News. Patrons of the restaurant sheltered in the basement until police arrived.
Police also reportedly responded to a third stabbing incident at Vauxhall, about one mile away, that was subsequently classified as unrelated.
Approximately two hours after the van plowed into pedestrians, Metropolitan Police tweeted: "At 0025hrs 4/6/17 the incidents at #LondonBridge & #BoroughMarket were declared as terrorist incidents."
The attacks come during Ramadan and a week before British elections.
Police have confirmed there were multiple fatalities.
All transit in the vicinity of the incidents was halted by authorities
BBC reporter Holly Jones, who was on the bridge at the time of the attack, described the van with a male driver behind the wheel, as "probably traveling at about 50 miles an hour."
"He swerved right round me and then hit about five or six people. He hit about two people in front of me and then three behind," Jones said.
The van was traveling from the direction of central London, headed toward the south side of the river, around 10:30 p.m. local time.
Jones reported seeing a handcuffed, shirtless man arrested by police. Thee BBC reports police are searching for three suspects who could be armed.
SkyNews showed police taking a man dressed in black into custody.
A similar attack occurred in London March 22, when a knife-wielding man mowed down pedestrians on London's Westminster Bridge before fatally stabbing an armed police officer to death just inside the gates of Parliament. Five people, including the attacker, were killed in that incident and approximately 40 injured.
Prime Minister Theresa May is scheduled to chair a meeting of the government's Cobra emergency-response committee on Sunday.
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