Chaos erupted in London late Saturday when a vehicle rammed into pedestrians on London Bridge, injuring an undetermined number of people and causing hundreds of others to flee in panic.
Shortly after midnight local time, London's Metropolitan Police Service tweeted that the violent episodes on the bridge and a nearby nightlife area were being treated as "terrorist incidents."
Earlier, Prime Minister Theresa May said the incident was being treated as a "potential act of terrorism," British media reported. The BBC reported that there had been more than one fatality, and that 20 people were being treated at a nearby hotel.
As authorities searched for suspects, the police announced on Twitter that officers were also responding to reports of stabbings in Borough Market _ not far from the bridge. Police reported shots had been fired.
Holly Jones, a BBC reporter who happened to be at the bridge when the incident occurred about 10:30 p.m., said a van had swerved off the road into a crowd of pedestrians.
"A white van driver came speeding _ probably about 50 mph _ veered off the road into the crowds of people who were walking along the pavement," she told BBC News.
"He swerved right around me and then hit about five or six people. He hit about two people in front of me and then three behind."
City transportation officials announced traffic on the bridge was shut down in both directions.
If a terror strike as suspected, this would be the third such attack in Britain in the last three months.
For those enjoying a Saturday night out in London, an evening's revelry quickly turned to a frightening ordeal. Paige Jegermanis, a 22-year-old American living in London, said soon after the bridge episode, a bartender informed the crowd in a riverside pub: "We're all on lockdown."
Then, half an hour later, they were asked to leave. The scene outside was "absolutely insane," she said. "Cop cars were going by, sirens on, people were running, I was crying."
Calum Curry told CNN that he and friends were walking near the bridge Saturday night when he heard a loud noise.
"We saw a car and a few bodies," Curry said. "Police flooded the area really quickly. ... We heard a bit of gunshots."
London Mayor Sadiq Khan issued a statement calling it "a deliberate and cowardly attack on innocent Londoners and visitors to our city."
"I condemn it in the strongest possible terms. There is no justification whatsoever for such barbaric acts," he said.
President Donald Trump tweeted that the United States was ready to help.
Last month, 22 people were killed and more than 59 others were injured in an explosion outside an Ariana Grande concert in the British city of Manchester that police said was caused by a bomber carrying an improvised explosive device.
The explosion happened near an entrance to the 21,000-seat arena just minutes after Grande's concert ended.
In March, an assailant drove a car into pedestrians on Westminster Bridge in London, killing two, and then stabbed a police officer to death before being shot to death himself.
This spring the U.S. Transportation Security Administration issued a report titled "Vehicle ramming attacks: Threat landscape, indicators and countermeasures," which notes that in the last three years, at least 173 people have been killed and more than 700 wounded in 17 ramming attacks around the world.
In December, a Tunisian man with ties to Islamic State deliberately drove a 27-ton truck into a Christmas market in Berlin, killing 12 people and wounding 56 others. And in July, as thousands crammed into the streets of Nice, France, for a Bastille Day celebration, another assailant influenced by Islamic State drove a 19-ton cargo truck into a crowd, leaving 86 dead and 434 injured.
The London attack comes at a politically sensitive moment. On Thursday, British voters are set to head to the polls for a general election. Last month, campaigning was briefly suspended in the wake of the Manchester attack.
