Bystanders have been hailed as heroes for preventing greater loss of life by tackling the man who went on a knife rampage on London Bridge. The attacker -- who had been released early from jail on terrorism charges -- killed two people and injured several more before police shot him dead.
The Islamic State armed group claimed responsibility for Friday's attack.
Video footage of the confrontation showed the knifeman, 28-year-old Usman Khan, being challenged by a man, reportedly a Polish chef, wielding a 1.5-metre narwhal tusk -- believed to have been grabbed from the historic hall where the stabbings began -- as another person sprayed him with a fire extinguisher and others came to assist.
"As we saw the worst of human kind, we saw the very best of human spirit and London," Metropolitan Police Commissioner Cressida Dick said Saturday as she visited London Bridge.
Khan had been conditionally released from jail last December after serving less than half of a 16-year prison sentence for terrorism, and was wearing a fake explosive device.
Police on Saturday searched two properties in Stoke-on-Trent, Khan's home city, and Stafford in central England.
The incident comes two years after Islamist extremists in a van ploughed into pedestrians on London Bridge before attacking people at random with knives in nearby Borough Market.
Eight people were killed and 48 wounded before the three attackers, who were wearing fake suicide devices, were shot dead by police.
Met Assistant Commissioner Neil Basu said in a briefing Saturday that five people were stabbed in total inside Fishmonger's Hall before members of the public pursued the attacker onto London Bridge. The three survivors remain in hospital.
Basu added that Khan had been released under "an extensive list of licence conditions" with which he had previously been complying.
Prime Minister Boris Johnson vowed to review the UK's sentencing system to avoid a repeat of another such incident.
"It does not make sense for us as a society to be putting people who have been convicted of terrorist offences...out on early release," Johnson, who became Tory leader in July, said as he visited the scene.
"We argue that people should serve the tariff, serve the term, of which they are sentenced," the prime minister added, noting the Conservatives' manifesto calls for a tougher sentencing regime.
Johnson said the cases of other convicted terrorists released early were under urgent review.
"A great deal of work is being done right now to make sure that the public is protected," he added.
The latest attack came less than two weeks before Britain's general election. Politicians have temporarily suspended campaigning.
'Bundle him to the ground'
Johnson spoke hours before the first victim of the attack was named as Jack Merritt, a course coordinator at Cambridge University's criminology institute, according to media reports.
The institute hosted a prisoner rehabilitation event at Fishmonger's Hall, a historic building said to contain many ancient artefacts on the north side of the bridge, which Khan attended reportedly armed with two knives and the fake suicide vest.
As the confrontation moved from inside the hall to the pavement outside, a throng of people could be seen in videos grappling with Khan.
They reportedly included a convicted killer on day-release from prison and other ex-offenders also attending the criminology gathering.
Tour guide Stevie Hurst told BBC radio that "everyone was just on top of him trying to bundle him to the ground.
"I saw that the knife was still in his hand so I just put a foot in to try and kick him in the head," he said.
A British Transport Police officer in a suit and tie who also intervened was later seen carrying a large knife away.