"Things need to change," Theresa May said on Sunday after the London attack, speaking outside of the prime minister's residence at 10 Downing Street.
London Metropolitan Police Commissioner Cressida Dick confirmed that seven people were killed in Saturday night's incident that saw a van mow down pedestrians on London Bridge before the vehicle's occupants got out and started stabbing patrons of nearby bars and restaurants. That toll does not include the three attackers, who were fatally shot by officers within eight minutes of the first emergency call, Dick said.
London Ambulance Service earlier said it had taken "at least 48 patients to five hospitals across London."
As doctors and nurses tended to the wounded, police carried out raids in the east London neighborhood of Barking in a signal that authorities are probing at least the possibility that others may have been involved in the attack's planning. A dozen people were arrested, police said.
The low-tech but high-profile attack will raise questions about how British security services failed to stop yet another mass-casualty strike after years of thwarting such attempts. May, who is running for another term in this week's general election, said the nation needs to step up its fight against radical ideologies in response, asserting that there is "far too much tolerance for extremism in our country."
The recent spate of terrorist attacks -- Saturday's was Britain's third in as many months -- were not connected, May said. But she described it as "a new trend" in which terrorists are "copying one another and often using the crudest means of attack."
May had returned from the campaign trail to 10 Downing Street late Saturday for emergency meetings with security officials. On Sunday morning, all the major parties, including May's Conservatives, suspended campaigning ahead of an election due on Thursday.
Labour leader Jeremy Corbyn said on Twitter: "Brutal and shocking incidents reported in London. My thoughts are with the victims and their families. Thank you to the emergency services."
Witnesses described a rampage that left a trail of bloodied bodies on the bridge and in the adjacent Borough Market, both London landmarks.
The attacks set off scenes of panic in the heart of London on a cool June evening as the city's streets were filled with people heading home from dinner or out for a drink.
In packed pubs -- normally scenes of Saturday night revelry and merriment -- patrons threw chairs, bottles and glasses at the attackers as the assailants used long knives to slash their way through crowds. Tourists gaped at the carnage from the roofs of double-decker buses.
London Mayor Sadiq Khan issued a statement condemning "a deliberate and cowardly attack on innocent Londoners and visitors to our city enjoying their Saturday night."
People in London should expect more police on the streets in the coming days, Khan said in a television interview on Sunday morning. But Londoners should not be alarmed and should not let terrorists disrupt daily life or the upcoming election, he said.
"We can't allow them to do that," Khan told Sky News. "We are not going to be cower by terrorism."
In a dawn news conference, Assistant Police Commissioner Mark Rowley said that the three attackers had been shot dead and that authorities did not believe anyone else was directly involved in carrying out the carnage.
Rowley said the men had not used explosives, despite a widely distributed photo that appeared to show one of the assailants lying prone with metal canisters strapped to his body. Rowley said the vest was "a hoax."
Saturday marks the third major attack in Britain this spring. The evening's carnage carried grim echoes of a similar incident in late March, when a driver swerved into pedestrians at Westminster Bridge, another Thames crossing, killing four. The driver then fatally stabbed a police officer at the gates of Parliament.
May had lowered the nation's threat level only days ago -- from "critical" to "severe" -- after having raised it following a bombing last month at a Manchester pop-music concert that was claimed by the Islamic State and that killed 22 people.
But even with the lower threat level, the nation's intelligence services had continued to judge that another attack was likely.
Also read: Second arrest in UK Tube bomb attack
The van collided with a guardrail. Bystanders said they thought the crash may have been an accident, until the occupants got out.
It was in the market, just south of the bridge, where police killed the attackers and ended the rampage.
"I heard many gunshots, and I heard people running away," said Joe Dillon, 23, who was nearby when the attack occurred. "Police officers were shouting: 'Get out of here, you need to go!' I heard at least eight rounds of gunshots, but I'm not sure who was shooting."
Tamara Alcolea, 24, a bartender in a pub called Southwark Rooms near the bridge, said the first indication that something was wrong was when she heard that someone had been stabbed close to London Bridge.
"Then we heard gunshots, and people started to hide beneath the tables," Alcolea said. "We locked ourselves in the office. From the window, I could see an injured person being treated by emergency personnel. Then the police came in and told us to run. Everyone was panicking."
As Alcolea recounted her story, she saw two friends whom she had lost track of during the melee. She cried and hugged them as they reunited outside a police cordon.
Chris Jacobs, 52, and his wife, Kavita Jacobs, 49, were woken by police officers banging on their door on the third floor of an apartment building at Borough Market.
"I heard gunshots as we left the building," said Chris Jacobs, who stood next to a gas station outside the cordon, with no shoes on and holding his dog.
Alex Shellum, an eyewitness, told the BBC he was at the Mudlark pub in the London Bridge area when at about 10 p.m. "a woman probably in her early 20s staggered into the pub and she was bleeding heavily from the neck and from her mouth. It appeared to myself and my friends that her throat had been cut."
Another witness, identified by the BBC as Gerard, said he saw three men running with knives: "They said, 'This is for Allah.' Then they ran up and stabbed this girl. I don't know how many times -- 10 times, maybe 15 times."
He said he and others threw whatever objects they could find -- including bottles, glasses and chairs -- at the attackers in a futile attempt to stop the rampage.
Within minutes of the attack, dozens of police cars sped to London Bridge and to Borough Market, with helicopters hovering overhead. Police closed the bridge and urged the public to avoid the area.
The incident caused chaos in the heart of London in an area normally bustling on a Saturday night. Pedestrians near the bridge said they were ordered by police to run, and video footage showed people fleeing in a panic. Other images showed members of the public being escorted away from the bridge by police with hands on their heads.
Two hours after the incidents began, police were still widening cordons and pushing bystanders farther back from the scenes as the sound of explosions -- apparently controlled blasts carried out by police -- echoed through the night.
President Donald Trump was briefed on the incident, and immediately took to Twitter to say: "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!"
After taking criticism online for trying to use the attack to advance a policy goal that is now under review in the courts, he sent a follow-up 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!"
The White House later issued a statement saying that Trump and May had spoken by phone and that the president had "offered his condolences for the brutal terrorist attacks."
On Sunday morning, Trump again took to Twitter with a series of messages that took aim at political correctness, the call in the United States for tougher gun laws and Khan, the London mayor. Trump chided Khan for attempting to calm the public by assuring that there was "no need to be alarmed."
A spokesman for the U.S. Department of Homeland Security said the agency was monitoring the incidents in London.
"At this time, we have no information to indicate a specific, credible terror threat in the United States," the spokesman said.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)