David Cameron said every action would be taken to restore order, with contingency plans for water cannon to be available at 24 hours' notice.
On Tuesday night, unrest spread to cities including Manchester, Salford, Liverpool, Nottingham and Birmingham.
Three men protecting property died when they were hit by a car in Birmingham.
Haroon Jahan, 21, Shahzad Ali, 30, and Abdul Musavir, 31, who were from the Asian Muslim community, were taken to hospital but died from their injuries.
Mr Cameron said the deaths were "truly dreadful" and offered his condolences to the men's families.
A candle-lit vigil, attended by some 200 people, took place in Birmingham for the men. The BBC's Jeremy Cooke said it was entirely peaceful.
Ladywood MP Shabana Mahmood had appealed for calm, telling a community meeting it was important people did not take matters into their own hands.
Meanwhile, rioters in Manchester and Salford have been told that they face being evicted from their council homes if they are identified on CCTV footage.
Both city councils have issued warnings that if any of their tenants or their children have been involved in violence or looting they will be "thrown out".
Greenwich Council also says it will be seeking the eviction of any council tenants if they are found to have been engaged in criminal activities.
Earlier, the prime minister said police had the legal backing to use any tactics necessary to bring the rioting across England under control, including using baton rounds.
Speaking after a meeting of the government's Cobra emergency committee, he said: "This continued violence is simply not acceptable, and it will be stopped.
"We will not put up with this in our country. We will not allow a culture of fear to exist on our streets."
But Association of Chief Police Officers (Acpo) president Sir Hugh Orde ruled out using water cannon or baton rounds for now, saying the tactics were not suited to the current unrest.
"Water cannon are used to deal with fixed crowds to buy distance," he said.
"The evidence... is showing very clearly these are fast-moving crowds, where water cannon would not be appropriate."
He added that baton rounds would only be deployed when his officers' lives were under serious threat.
Meanwhile, Home Secretary Theresa May told the BBC she had ordered all police forces in England and Wales to mobilise special constables, cancel leave and adopt a "tough, robust approach".
Six forces have requested assistance for Wednesday evening, according to Acpo, which is co-ordinating resources in England and Wales.
They are Avon and Somerset, Gloucestershire, Greater Manchester Police, the Metropolitan Police, Nottinghamshire, and West Midlands.
By Jon BrainBBC News, Highbury Corner Magistrates' Court
Sitting in the dock in a blue tracksuit top, the 11-year-old boy was barely big enough to see over the wooden ledge into the main body of the courtroom.
But, according to the prosecution, the child had been among the hundreds arrested in connection with the rioting in London over the past few nights.
He was the youngest to appear at Highbury on Wednesday, and admitted taking a wastepaper basket from a branch of Debenhams in Romford, which was looted by rioters.
Others brought before magistrates included a man who works in a primary school, a student and a convicted drug dealer. Nearly all will be sentenced at crown courts which have the powers to impose tougher penalties.
The 11-year-old is due at a youth court at the end of the month. Despite his tender age, he spent last night in a police cell. He's been told to observe a curfew between 18:00 and 06:00 until his fate is decided.
Analysis: Courts run all night
Earlier, Mr Cameron said: "We have seen the worst of Britain, but I also believe we have seen some of the best of Britain - the million people who have signed up on Facebook to support the police, coming together in the clean-up operations.
"There are pockets of our society that are not just broken, but are frankly sick.
"It is a complete lack of responsibility in parts of our society, people allowed to feel the world owes them something, that their rights outweigh their responsibilities and their actions do not have consequences. Well, they do have consequences."
The Met Police has made 820 arrests and charged 279 people in connection with violence in the capital.
In London, three courts will stay open all night on Wednesday to deal with some of the scores of people facing mainly disorder and burglary charges after four nights of rioting.
In other developments:
Mr Cameron said anyone convicted of violent disorder would be sent to prison.
London mayor Boris Johnson urged the government to reconsider its "pretty frail" plans to cut police numbers, saying the argument had been "substantially weakened" by the riots.
And Labour shadow home secretary Yvette Cooper said agreed, adding the plans needed to be reconsidered.
"It is staggering and utterly shameful if it has taken these appalling events for ministers to start waking up to what everyone else has known all along," she said.
"Cutting 16,000 officers - the equivalent of every officer on the streets of London last night - at a time like this is deeply irresponsible."
But the Home Office said the reductions in the police budget were manageable.
At a press conference, Greater Manchester Police's Assistant Chief Constable Garry Shewan said he had seen "the most sickening scenes" of his career, and said the force had been overwhelmed.
Source: Acpo
Some 113 people have been arrested so far over the trouble in Manchester and Salford, where hundreds of youths looted shops and set fire to cars and buildings.
He said the force was "absolutely intent" on bringing the rioters to justice and his officers were already studying CCTV.
"Hundreds and hundreds of people, we have your image, we have your face, we have your acts of wanton criminality on film. We are coming for you, from today and no matter how long it takes, we will arrest those people responsible," he said.
In the West Midlands, 163 people had been arrested by Wednesday morning, and police chiefs say at the height of the disorder it was at a rate of about one person per minute.
Chief Constable Chris Sims said it was "another very difficult night" in Birmingham and across the region, with gangs of up to 40 people and "limited disorder" in West Bromwich and Wolverhampton.
The riots first flared on Saturday after a peaceful protest in Tottenham over the fatal shooting of Mark Duggan, 29, by police.
The prime minister has said the "fightback" is under way, after cities in England suffered a fourth night of violence and looting.