The mayhem began just after 10 p.m. (2100GMT), when police responded to reports of a vehicle hitting pedestrians on London Bridge, which crosses the River Thames in central London.
Police also are reporting a potential incident in the Vauxhall area of southwest London.
It was the third terror attack to strike the United Kingdom this year, after a man drove a vehicle into pedestrians on Westminster Bridge in March and the bomb attack on an Ariana Grande concert in Manchester two weeks ago.
"We are dealing with an incident on #LondonBridge, when we have more information we will update this twitter feed". Armed officers responded and shots were fired. "I want to express my huge gratitude to the police and emergency services who are on the scene", May added. It is too early to say this is a terror incident, but although we have seen this before. She will chair a meeting of the UK's response group Cobra tomorrow.
The Royal Oak pub, near the attack site, opened its doors to people evacuated from hotels inside the area cordoned off by police. I condemn it in the strongest possible terms. At the time of the attacks, authorities tweeted a warning telling people in the area to run to safety, hide and call police. They asked Londoners to "remain calm but be alert and vigilant".
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"Officers jumped out and started tending to the guy on the floor and about three of them also started running towards the London Bridge area".
"It's horrific, they took us past them, it's horrific the ambulances are taking them out". An advanced trauma team was also sent by auto. The patrons sheltered in the basement until police arrived.
The seriousness of the injuries is not yet known, he said. The legal fight pits the president's authority over immigration against what lower courts have said is a policy that purported to be about national security but was meant to target Muslims.
Casualties were seen being taken away from Tito's restaurant on London Bridge Street with blood on the steps of the eatery. "He came down the stairs and went to the bar", Dee, 26, who was visibly in shock and declined to give her last name, told AFP. A BBC reporter who was on the bridge at the time said the van was driving around 50 miles per hour.
It swerved into oncoming lanes before hitting a bus stop and coming to a stop, Roberts said. Eyewitnesses told The Sun that several people were stabbed by "two to three men armed with 12-inch-long knives".
"A police officer was trying to put himself between them and the crowd". Mostly young people, many of them in tears.