Updated at 16:45
Britain's NHS (National Health Service) has warned that 21 of those injured in last night's terror attack in London are currently in a "critical condition."
At least seven people were killed and 48 injured in central London after attackers drove a van into pedestrians before stabbing others nearby.
In a statement this afternoon, London Met Police Chief Mark Rowley said 36 people currently remain in hospital receiving treatment.
He said authorities are "increasingly confident" the attack was conducted by three individuals although he cautioned that "clearly we need to establish whether there are any associates or anyone else involved in the planning."
Attackers drove a van at high speed into pedestrians on London Bridge just after 10pm on Saturday night before continuing to drive from the bridge to Borough Market.
There, they jumped out of the van and stabbed people, including a British Transport Police officer who has serious but not life-threatening injuries to his face, head and leg.
Within eight minutes, armed police confronted three male attackers, shooting them dead in Borough Market.
Six of those who were killed died at the scene, where a number of others were treated for minor injuries.
A Canadian national is among the dead.
Among the injured being treated in hospital are those believed to have confronted the attackers, including a British Transport Police officer who faced the men with only his baton.
"I can confirm that eight police firearms officers discharged their weapons," said Assistant Commissioner Rowley this afternoon. "While this will be subject to an investigation by the the IPCC, our initial assessment is [...] in the region of 50 bullets were fired by those eight officers."
"The three attackers were shot dead.
"The situation these officers were confronted with was critical - a matter of life and death; Three armed men wearing what appeared to be suicide belts.
"They had already attacked and killed members of the public and had to be stopped immediately. Indeed I am not surprised that when faced with what they must have feared were suicide bombers the firearms officers fired an unprecedented number of rounds.
"I am humbled by the bravery of an officer who will rush towards a suicide bomber thinking only of the safety of others.
12 people have been arrested in connection with the attack.
In a statement London's Metropolitan Police said: "Officers from the Met's Counter Terrorism Command have arrested 12 people in Barking, east London, in connection with last night's incidents in London Bridge and the Borough Market area."
They also said that "searches of a number of addresses in Barking are continuing."
"Tolerance of extremism"
Earlier, British Prime Minister Theresa May said there is "a new trend of terrorism" in the UK and that "terrorism breeds terrorism."
Mrs May addressed the media outside Downing Street this morning, after the UK's emergency COBRA meeting.
She said there is too much tolerance of extremism in the UK and that it's time to be more robust in tackling it.
She also confirmed that the UK General election will go ahead as a planned on Thursday.
London Mayor Sadiq Khan said: "We don't yet know the full details but this was a deliberate and cowardly attack on innocent Londoners and visitors to our city enjoying their Saturday night. I condemn it in the strongest possible terms.
"There is no justification whatsoever for such barbaric acts."
The attacks come less than two weeks after a suicide bomber killed 22 people at a concert in Manchester.