Parliament will be recalled on Thursday in response to rioting in England, prime minister David Cameron has said.
The government's emergency committee Cobra met on Tuesday after rioting spread across London, with violence flaring in other major cities.
The Metropolitan Police has cancelled all leave, with more than 16,000 officers due on London's streets later.
The force says it is considering the use of plastic bullets - never before fired to deal with riots in England.
Deputy Assistant Commissioner Stephen Kavanagh said their use would be "considered carefully" but added: "That does not mean we are scared of using any tactic."
Acting Commissioner Tim Godwin had earlier ruled out calling in the Army.
Meanwhile, Scotland Yard said a 26-year-old man found shot in a car in Croydon, amid rioting in the south London town, had died in hospital.
Mr Cameron met officers in the Met Police's Gold command in Lambeth on Tuesday afternoon, before speaking to emergency service personnel in Croydon.
He condemned the "sickening scenes of people looting, vandalising, thieving, robbing", which the Met Police said had resulted in 525 arrests and more than 100 people being charged.
He told rioters: "You will feel the full force of the law. And if you are old enough to commit these crimes, you are old enough to face the punishment."
The recall of Parliament will allow MPs to "stand together in condemnation of these crimes and to stand together in determination to rebuild these communities", he said.
The prime minister returned early from his holiday in Tuscany to discuss the unrest, which first flared on Saturday after a peaceful protest in Tottenham over the fatal shooting of a man by police.
London has seen a wave of "copycat criminal activity" over the past three days, the Met Police said. More than 69 people have been charged with various offences following hundreds of arrests.
Birmingham, Liverpool, Nottingham and Bristol are among the other cities where violence broke out.
Shops have been looted across the capital
In other developments:
* Three people are being questioned on suspicion of attempted murder after a police officer was injured by a car in Wembley, north-west London, while trying to stop suspected looters
* Part of London's Tramlink between has been suspended as a result of a fire
* Elsewhere, 138 people have been arrested in Birmingham after scores of youths smashed windows and looted shops in the shopping area
* West Midlands Police said a police station in Holyhead Road in Handsworth, Birmingham, was set alight
* Up to 200 youths with masks roamed through Toxteth in Liverpool, while Bristol police said they dealt with outbreaks of disorder involving about 150 people
* A Nottinghamshire police station was attacked in the St Ann's area and 200 tyres were set alight in the street
* Police dealt with "small pockets of disorder" in the Chapeltown area of Leeds
Monday's violence started in Hackney, north London, after a man was stopped and searched by police, who found nothing.
Groups of people there began attacking officers in Hackney at about 16:20 BST, throwing stones and a bin.
Police cars were wrecked by youths armed with wooden poles and metal bars, while looters smashed their way into shops before police dispersed them.
Nine other forces are supporting the Metropolitan Police, as well as the City of London Police and British Transport Police.
Special constables and community support officers will also swell the ranks to ensure more than five times the usual number of officers for a Tuesday will be on duty.
Some people had complained there were too few police to deal with the violence.
The Met said Monday's was "the worst" disorder in "current memory" after incidents across the capital.
* Several fires broke out in Croydon, including one at a sofa factory which spread to neighbouring buildings and tram lines
* Hackney MP Diane Abbott said a London-wide curfew should be considered after 200 riot officers with dogs and mounted police were needed to deal with violence there
* Looters raided shops in Stratford High Street and Clapham Junction, where police used armoured vehicles to push back more than 150 people
* A Sony warehouse in Enfield, a shopping centre in Woolwich New Road and a timber yard in East Ham were all on fire
* Police said two officers were injured when more than 100 people looted a Tesco store in Bethnal Green, while vehicles were set alight in Lewisham and Peckham
* There were reports of looting of phone shops in Woolwich High Street, in south-east London, and set a police car on fire
* Shops and restaurants were damaged in Ealing, west London
* Tuesday's Carling Cup matches at Charlton, West Ham, Crystal Palace and Bristol City have been postponed at the police's request
* England and Holland's friendly at Wembley on Wednesday was also called off has also been called off
Hackney resident Catherine Holmes said: "Our community has been hurt and damaged by causeless violence. We spoke to looters trying to get home - the only explanation they gave for their behaviour was that they had no money."
Christian Potts, 29, described Ealing as "like a war zone".
"There were about 25 to 30 masked youths on Haven Green and they just started tearing into a florist with bricks. It's a local family-run business so I can't see why they are doing this."
London's mayor Boris Johnson cut short his holiday to return to the city, while Home Secretary Theresa May did the same to meet Met chiefs.
"These have been the worst scenes of violence and disturbance on our streets for many, many years, and this sort of violence, this level of criminality, this thuggery, this looting, this theft, is completely unacceptable," Ms May told BBC Breakfast.
However, she said the authorities could deal with the situation through robust policing, good use of intelligence and with the support of local communities.
She called on anyone involved in the violence to speak to police.
The trouble follows two nights of violence over the weekend which started after police shot a man dead in Tottenham.
A peaceful protest in Tottenham on Saturday over the death of Mark Duggan, 29, was followed by violence which spread into this week.