A Scotland Yard chief apologised to Londoners today as he said the riots had stretched resources "to an extent I have never seen before".
The arrest toll soared to 525 this afternoon as it emerged the escalating violence had claimed its first life.
Deputy Assistant Commissioner Stephen Kavanagh said he apologised "that London has got to wake up to these scenes".
"We need to do better for London because those images last night were shocking for everyone," Mr Kavanagh told reporters.
Mr Kavanagh said: "From 4pm yesterday evening the extremely mobile level of violence meant that resources were stretched to a level I have never seen before."
From this afternoon, up to 16,000 officers will be on duty, he said, adding that every beat officer and police community support officer "needs to be standing next to their community".
Giving an update on arrests, Commander Simon Foy issued a warning that the police will mount a "vigorous and rigorous pursuit" of individuals who have not been arrested and "think they have got away with it".
"My message to them is we will come and find you."
The Lancashire and Greater Manchester Police forces have sent support units to aid the Metropolitan Police.
Around 100 officers from Greater Manchester Police trained in dealing with public disorder were deployed to London earlier.
More than 30 officers from three police support units (PSUs) of Lancashire Constabulary and a Public Order Commander are also assisting, along with colleagues from Cumbria Constabulary.
Assistant Chief Constable Peter White, of Lancashire Constabulary, said: "We can confirm that we are providing mutual aid to the Metropolitan Police Service during the ongoing disturbances in and around London.
"Three Lancashire Police Support Units - a total of 33 officers - have been deployed along with a Public Order Commander to assist colleagues in the Met with the operation.
"We would reassure the public of Lancashire that the constabulary's ability to deal with and prevent crime during this time will not be affected.
"While we have not cancelled rest days or annual leave at present, we have made a decision not to approve any new requests for leave or rest days for the duration of the operation in London."
Cumbria Constabulary said it had committed to providing mutual aid to the Police National Information Co-ordination Centre.
A spokeswoman said: "Around 30 highly-trained police officers from Cumbria are currently on stand-by and ready to be deployed to support colleagues in other force areas.
"Cumbria Constabulary also has contingency plans in place to ensure that there are enough available resources in Cumbria."
Business Secretary Vince Cable told BBC Radio 4's World at One the public were looking for "absolute assurance" that people engaged in the violent, thuggish behaviour were arrested and where found guilty "suitably punished".
He said: "I am in close touch with all the business groups to make sure that those people in the affected areas are given the support they want."
Mr Cable said nobody expected the disturbances would break out "all over London in the way they did".
Commenting on the reasons for the riots, he said: "All the evidence so far is that this is criminality, it is theft, there doesn't appear to be any underlying political purpose in it."
He added there was a need to get to the bottom of the "complex causes".
Commander Simon Foy said the events of last night had been "very shocking" to the Met and communities in London.
He said the Met had been stretched in the past couple of days "as it's never been before" and police numbers had now been increased to a level it was hoped was "appropriate to deliver a safe London".
He added: "The events yesterday stretched us as I've said before, like we've never been stretched in our history. It was the scale, the nature, the spread of events over so many places."
There were more than 500 detectives working for him on the investigation, he said.
He added: "We have lots of information to suggest that there may be similar disturbances tonight. That's exactly the reason why the Met has chosen to now actually really 'up the game' and put a significant number of officers on the streets."
Commander Foy said the Met had "looked very closely during the night at every possible tactic that is available to us" from the use of baton rounds, to water canon, to CS spray to CS gas.
He said the events needed to be dealt with by the Met Police "doing what it normally does in policing London", adding it would be an "absolute tragedy" if officers had to revert to using "exceptional powers" to help get things back to normal.
He said: "We honestly believe that we think we can do it using the powers that we have at the moment."
Mr Kavanagh said last night's scenes of violence "stretched people in a way they have never been stretched before and it tested people in a way they have never been tested before".
He added: "I utterly regret the scenes that I saw on the television through the night, we put out more officers than we ever have before.
"Today what is happening is the Met is mobilising every single person, there will be no leave, there will be no other types of investigation other than the utmost serious ones.
"This means that we can't continue to do the business in the way that we want to be doing it for next 72 hours, this is about us recognising this is unprecedented, the nature and extent of the violence last night."
Mr Kavanagh said that 43,000 calls came into the Met's information room last night, of these, 25,000 required immediate attention.
Mr Kavanagh said the police need to work with communities to deal with the rioting, adding that children as young as 11 were arrested for looting last night.
"We have to work with communities because this is not going to be about the Metropolitan Police solving this, this is not going to be about baton rounds or baton charges, this is going to be about mobilising communities because actually we are seeing a kick back.
"They're angry, we're seeing it on Twitter, we're seeing it in conversations that we're having with communities. This is their jobs that are at stake, this is their homes and their buildings and I think we're going to do this with communities."
Asked about the use of tactics like baton rounds, Mr Kavanagh said: "I think I've been pretty clear that the Met Police does not wish to use baton rounds but if it gets put into a position that it needs to protect the people and the property and the lives of Londoners that we will do so."
He added: "We had people as young as 11 being arrested for looting last night, do we genuinely want to see the police of London using that type of tactic on 11-year-olds? We have to be very careful about what we use and how we're using it.
"What we're saying is we cannot rule anything out and we cannot be fearful because the people who have these businesses, the people who have these homes need to know that the police service is going to be with them tonight, and tomorrow and the next day and we need to deal with these, they are thugs, they are criminals, together."
Mr Kavanagh said he was not trying to claim that last night's policing of the riots was a success.
"What I'm saying is I'm not going to turn round to the officers who described consistently taking those bricks and bottles trying to arrest those individuals, getting assaulted, that they failed.
"What I'm saying is the Met got stretched in a way that we've never experienced and we can't sit here and say that that scale of violence, that intensity, that speed of movement has ever been seen in the UK or Europe before."
The Metropolitan Police will be using "every part of its body" to ensure that the disorder tonight is minimised, Mr Kavanagh said.
On a usual night around 2,500 response officers are on duty, he added.