"We needed a fightback and a fightback is under way", the Prime Minister has said after four days of riots.
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, with shops being looted and set alight.
Three men died when they were hit by a car in Birmingham.
Mr Cameron, speaking after a meeting of the government's Cobra emergency committee said police were authorised to take "any action necessary" to bring the situation under control.
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.
"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."
The PM said more arrests would take place as police worked through CCTV evidence. "Picture by picture, the criminals are being identified and arrested," he said.
'We have your face'
Earlier, London Mayor Boris Johnson urged the government to reconsider its plans to cut police numbers, saying the argument had been "substantially weakened" by the riots.
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.
Speaking at a press conference on Wednesday morning, he said force was "absolutely intent" on bringing the rioters to justice and 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.
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.
In the West Midlands, 109 have been arrested and 23 charged following scenes of disorder in Birmingham, Wolverhampton and West Bromwich - where vehicles were set on fire.
Meanwhile, West Midlands Police are to question a 32-year-old man on suspicion of murder after three men were run over and killed.
One of the victims has been named as Haroon Jahan. His father Tariq Jahan paid tribute to him, saying he "had his whole life ahead of him".
In other developments:
Canning Circus police station in central Nottingham was firebombed by a male gang on Tuesday evening. Nottinghamshire Police said 90 people had been arrested
In Liverpool, Merseyside Police have arrested 50 people in relation to disorder in the city
Nine people have been arrested in Gloucester after police officers came under attack from youths throwing stones and bottles from 23:00 BST
In Leicester, a group of up to 100 youths attacked shops and threw items at police, with 13 arrests
In Bristol, police arrested 19 people following a second night of trouble
Thames Valley Police made 15 arrests linked to trouble overnight
Metropolitan Police have arrested 768 people and charged 105 in connection with the violence in the capital, including a 21-year-old man who was arrested on suspicion of arson with intent to endanger life following a fire which took hold of the Reeves Furniture store in Croydon on Monday night
Officers from all eight Scottish Police forces are being sent to help colleagues in the Midlands and North of England deal with rioting and looting
A 26-year-old man found shot in a car in Croydon, amid rioting in the south London town, has died in hospital
Government minister Michael Gove has praised the Met's response to the riots, saying bringing in an extra 10,000 officers helped to prevent further riots from taking place in London
Meanwhile, two 18-year-olds in Folkestone, Kent, and a 19-year-old woman in Wakefield have been arrested. A 16-year-old boy in Glasgow was charged with breach of the peace while another man, aged 18, has been arrested. All relate to allegations of inciting violence through internet social networking sites
The Independent Police Complaints Commission (IPCC) said on Tuesday that ballistic tests presented "no evidence" that a handgun found at the scene where Mark Duggan, 29, was killed in Tottenham had been fired at officers
Wounded officers
Scotland Yard drafted in special constables and community support officers in London to ensure five times the usual number of officers for a Tuesday - 16,000 - were on duty. They made 81 arrests.
Asst Chief Constable Garry Shewan: "We have your image, we have your face ... we are coming for you"
Downing Street said the increased level of policing would remain in place "as long as necessary" to prevent a repeat of the violence.
It said while there was "no complacency," police tactics in London had "clearly worked".
It followed three nights of rioting in the city which saw shops looted, property set alight and police attacked, with some 111 Met officers suffered injuries including serious head and eye wounds, cuts and fractured bones after being attacked by rioters wielding bottles, planks, bricks and even driving cars at them. Five police dogs have also been hurt.
The Met's Deputy Assistant Commissioner, Stephen Kavanagh said London deserved "some resilience and sustainability from police".
'Rapid response'
Referring to proposed police cuts, London Mayor Boris Johnson said: "That case was pretty frail and it's been substantially weakened. This is not a time to think about making substantial cuts in police numbers."
But the Home Office said the reductions in the police budget were manageable.
Labour leader Ed Miliband called for a "rapid response" from the government to help affected communities.
He urged the government to work with the insurance industry "to put in place fast-track procedures with immediate effect so that individuals and businesses making claims do not have to wait for the money they need to start putting things right".
The Association of British Insurers says the damage is likely to cost insurers "tens of millions of pounds".
The riots first flared on Saturday after a peaceful protest in Tottenham over the fatal shooting of Mark Duggan, 29, by police.