At least seven people have been confirmed dead after three attackers drove a van into pedestrians at high speed on London Bridge before stabbing multiple victims at nearby Borough Market.
Metropolitan Police Commissioner Cressida Dick told media on Sunday morning London time that the death toll had risen to seven after the "appalling and tragic" attack the night before.
“It has now been confirmed sadly that seven members of the public have died. In addition, as you know, we believe, three suspects are dead,” she said in a televised statement.
Another 48 people are being treated at five London hospitals following the incident, which UK Prime Minister Theresa May has described as a terror attack.
Armed police responded to the attack within eight minutes, shooting dead the three attackers as emergency services scrambled to treat the wounded.
Far too much tolerance of extremism, says May
When asked if she knew the identity of the attackers she replied, "I don't".
Ms Dick said the police were conducting a fast moving investigation and the priority now was to work with counter-terrorism police colleagues to establish more details about the attackers.
Dick said police believed the incident was under control, but officers needed to conduct a thorough search of the area to ensure everyone was accounted for and no further suspects were at large.
"Our priority now is to work with our colleagues in the national counter-terrorism police network and also with the intelligence agencies and other security services to establish more details about these individuals who carried out the attack and the background to it," she said.
She added the police would deploy increased patrols including armed officers.
London Bridge victims receive emergency CPR
Metropolitan Police Assistant Commissioner Mark Rowley said an investigation has been launched into the attack, and has called for calm.
He added that the three attackers were wearing what appeared to be explosive vests, but which were later revealed to be fake.
"At this stage, we believe that six people have died in addition to the three attackers shot dead by police," he said.
“I’d like to repeat our request for Londoners to avouid the London Bridge and Borough Market area.
“Our current belief is that there were three attackers. But the investigation is in an early stage and we still have some more inquiries to do.”
Prime Minister Theresa May is expected to chair a meeting of the government's emergency response committee on Sunday local time.
Her Conservative Party suspended national campaigning on Sunday for the upcoming June 8 UK election, a spokesman for May said following an attack in London which killed six people.
"The Conservative Party will not be campaigning nationally today. We will review as the day goes on and as more details of the attack emerge," the spokesman said.
Labour Party Leader Jeremy Corbyn joined her, saying his party would suspend campaigning until Sunday evening.
Earlier Ms May said the incident was a suspected terror attack.
“Following updates from police and security officials, I can confirm that the terrible incident in London is being treated as a potential act of terrorism," Ms May said.
A spokesperson for the Scottish National Party said its campaign activity would also be suspended.
“This is a fast moving investigation. I want to express my huge gratitude to the police and emergency services who are on the scene. Our thoughts are with those who are caught up in these dreadful events.”
While the leader of the UK Independence Party Paul Nuttall said on Sunday he would not be suspending election campaigning.
London Mayor Sadiq Khan said he did not advocate postponing the imminent election.
People running from the scene at London Bridge
The attack occurred with the UK still reeling from a bombing in the northern town of Manchester last week in which 22 people were killed.
They also came just days before Britain goes to the polls for a general election on Thursday.
Witnesses on London Bridge reported seeing a van mounting the pavement and hitting pedestrians and a man running with a knife.
"There was a van that crashed into the fences on London Bridge. And then there was a man with a knife, he was running," said Dee, 26, who was visibly in shock and declined to give her last name.
"He came down the stairs and went to the bar."
Gerard Kavanar, 46, said he had seen a chef with "blood on his shoulder" in the area.
The London Ambulance Service said "multiple resources" were being sent to the scene.
The police were urging the public to run to a place of safety, or hide if they cannot.
AFP reporters saw two police helicopters over the area and several roads were shut down.
'Wounded people'
Will Heaven, managing editor of The Spectator magazine, said on Twitter that he saw "two casualties - one on pavement, one edge of road" and reported seeing armed police on the bridge.
BBC reporter Holly Jones, who was there at the time of the incident, said she saw a van driven by a man travelling "at about 50 miles (80 kilometres) an hour".
She said about five people were being treated for injuries after the vehicle mounted the pavement and hit them.
"There's several police boats with torchlights searching the Thames at the moment," she told BBC radio.
She added that she saw a man, who had his shirt off and was in handcuffs, being arrested by police.
Another witness, Alessandro, told BBC radio that he saw a van strike several people on London Bridge.
"I saw this van going left and right, left and right, trying to catch as many people as he could. And people just tried to get out of the way of the van.
"Then I tried to help people, wounded people."
Of the casualties, he said: "Three of them, yes (were conscious), and one guy was not talking at all, was just, like, down."
"There were five or six people that we tried to help, they were young people."
His friend Giovanni said he contacted police and the ambulance services, which arrived within around two minutes.
Simon Johnson, who had been near London Bridge, told Sky News he had hid in the basement of a restaurant in the area for about an hour.
"Still in a state of shock to be honest," Johnson said.
'Large blade'
Husband and wife Ben and Natalie told BBC Radio 5 Live they were outside Borough Market when they witnessed the incident there.
Ben said: "We saw people running away and then I saw a man in red with a large blade, at a guess 10 inches long, stabbing a man, about three times.
"It looked like the man had been trying to intervene, but there wasn't much he could do. He was being stabbed quite coldly and he slumped to the ground."
Ben said the man then walked towards the Southwark Tavern. He said they saw a metal chair being thrown towards the man.
"Then we heard three gunshots, definitely gunshots, and we ran."
The incident is reminiscent of the March 22 Westminster Bridge terror attack in the city in which five people were killed and more than 50 wounded.
The assailant in that attack, 52-year-old British Muslim convert Khalid Mahmood, rammed his car into pedestrians before crashing into the barriers surrounding parliament and then stabbing a police officer to death.
He was then shot dead by police at the scene. Investigators later described the lone-wolf attack as "Islamist related terrorism".
It also comes less than two weeks after 22 people, including seven children, were killed in a suicide bombing at the end of a pop concert at the Manchester Arena.
Manchester-born Salman Abedi, a 22-year-old of Libyan origin, was named as the Manchester bomber.
