Two people have been killed in a stabbing attack in central London, and the suspect shot dead by police.
Metropolitan Police declared the attack a terrorist incident.
The attack started at Fishmonger's Hall in London, a conference venue located at the northern end of London Bridge, just before 2:00pm on Friday (local time).
Police said the attacker, who died after being shot multiple times at the scene, was wearing a hoax explosive device.
Metropolitan Police Commissioner Cressida Dick confirmed in a press conference that two people who were attacked by the man have died.
Three others were injured in the attack, police confirmed.
Video posted to social media shows several members of the public wrestling with the man on London Bridge before armed police officers arrive on the scene.
The armed officers then separate the group before firing two shots at the suspect as he lays on the ground.
Commissioner Dick said she could not comment on whether the suspect was known to police but police would be investigating whether the suspect was a lone wolf attacker or part of wider network.
"That's obviously a very important line of investigation for us. 'Was this person involved with anybody else? If so, who?' And, of course, we will be working to minimise any threat there may be out there," she said.
"We will be working as fast as we can to understand who this man is, where he came from, and whether there is anybody else that we need to find quickly who might be in touch with him."
Appealing for anyone who witnessed the incident or had video footage of the attack to come forward, she said police were working to identify the two victims and notify their families.
Assistant Commissioner Neil Basu, the head of the UK's counter-terror policing, said there were reports the suspect may have had an explosive device so specialist police were deployed and wide cordons put in place to protect the public.
"I can confirm that at this time, we believe a device that was strapped to the body of the suspect is a hoax explosive device," he said.
"Officers continue to carry out meticulous searches in the area to ensure there is no outstanding threat to the public."
BBC News reporter John McManus was walking across London Bridge when he saw part of the incident unfold.
"There appeared to be a fight going on on the other side of the bridge, with several men attacking one man," he told the BBC.
"Police then quickly arrived, including armed police, and then a number of shots were fired at this man."
Police could be seen ushering people away from the northern end of the bridge, which links the city's business district with the south bank of the River Thames.
Cars and buses on the busy bridge were at a standstill, with a white truck stopped diagonally across the lanes as it tried to turn around.
Cambridge-based prison-education organisation Learning Together was holding an event at Fishmonger's Hall at the time of the attack.
The University of Cambridge said it was "gravely concerned" about students, staff and alumni who might have been caught up in the incident.
The Australian High Commission in London is not aware of any Australians affected by the incident.
British Prime Minister Boris Johnson hailed emergency services and members of the public who intervened "to protect the lives of others".
"They represent the very best of our country and I thank them on behalf of all of our country," he said.
He also said anyone involved in the attack would be "hunted down and will be brought to justice."
"I think the message that we send to them and anyone associated with this type of attack is one that will be familiar, and that is that this country will never be cowed or divided or intimidated by this sort of attack," he said.
The Conservative Party and Labour have both said they will suspend their respective election campaigns in London in the wake of the attack.
London Bridge was the scene of a 2017 attack when Islamic State-inspired attackers ran down people on the bridge, killing two, before stabbing several people to death in nearby Borough Market.
