A man has been shot by police on London Bridge after a knife rampage which officers are treating as a terrorist attack.
Several people were stabbed by the knifeman before he was grappled to the ground and disarmed by members of the public.
Footage on social media appeared to showed one man being pulled away by armed officers moments before the suspect is shot at point-blank range.
Another bystander could be seen carrying a large knife from the scene.
The Met Police have announced at a press conference that the London Bridge incident has now been declared a terror incident, the suspect is dead, and a hoax explosive device was strapped to the suspect's body.
Neil Basu, the head of UK counter-terrorism policing, said: "At approximately 2pm today, police were called to a stabbing at a premises near London Bridge.
"Emergency services attended including officers from the City of London Police and Metropolitan Police.
"A male suspect was shot by specialist armed officers from City of London police and I can confirm that this suspect died at the scene."
Mr Basu said that specialist officers had been deployed after reports that the suspect had an explosive vest, but the device was believed to be a "hoax".
He said: "Due to reports that the suspect might have had an explosive device specialist officers attended the scene.
"However, I can confirm at this time we believe a device that was strapped to the body of the suspect is a hoax explosive device."
Mr Basu said he would give updates to the families of those injured "as soon as we can get that information".
He added: "A number of other people received injuries during this incident. As soon as we can provide further updates on their condition, we will.
"Our heartfelt sympathies go out to everybody who has been involved in this and is anxiously waiting for information on their loved ones.
"As soon as we can get that information, we will get it to you."
Yahoo News UK was told by one witness that the incident originated at Fishmonger's Hall, a conference and events venue on the River Thames near London Bridge.
The witness told Yahoo News over WhatsApp: "I was in the building when I heard the screams and one girl ran towards me because she got stabbed in her arm and everyone inside the conference started to panic.
"I think there is one person dead. A woman got stabbed a few times I believe. And then we were evacuated."
Ayala said she didn't know how many people were involved in the incident.
"I couldn't see. I heard it was only one," she said. "I heard about seven gunshots while I was evacuating the building. The gunshots were outside the building."
She said she saw "two, three people stabbed. One minor and the other two were proper bleeding".
Prime Minister Boris Johnson has said "anybody involved in this crime and these attacks will be hunted down and will be brought to justice" as he paid tribute to the "bravery" of the emergency services and members of the public who intervened in the London Bridge attack.
Mr Johnson, speaking in Downing Street, said the UK would "never be cowed or divided or intimidated by this sort of attack and our British values will prevail".
In a statement outside Scotland Yard, Sadiq Khan thanked members of the public who risked "their own safety this afternoon".
"I want to thank our brave emergency services who responded to today's horrific attack," the mayor told a press conference at Scotland Yard.
"Every day, they put their lives on the line for us, running towards danger in order to keep us safe.
"I'd also like to thank members of the public who risked their own safety this afternoon. They are the best of us."
Mr Khan asked all Londoners to remain vigilant and report anything suspicious to the police.
A White House spokesman said: "President Trump has been briefed on this morning's attack at the London Bridge and is monitoring the situation.
"The United States strongly condemns all horrific acts of violence on innocent people, and we pledge our full support to our ally, the United Kingdom."
Witness Cecilia Sodero was on the top deck of a bus going over London Bridge when she heard shots and saw a man lying on the ground with a "very scary device, like a bomb device".
"I was like okay, this is unusual, so me and the other passengers started looking outside, to see what's going on, and we saw like six people holding someone on the floor," she told Sky News.
"At some point someone says 'oh, he has a knife', and we were like, oh my gosh, this guy is supposed to stab someone and people was running away.
"The police officers finally they removed the knife. But then what happened is when they shot the guy, the guy is still alive, and they shoot and he's trying to pull the black jacket off so I was able to see the vest that he was wearing.
"And it seems like a very scary device, like a bomb device, at that point we just ran away from the bus, crossing the bridge in the other direction.
"The whole thing was very scary to be honest."