Rioting has spread across London on a third night of violence, with unrest flaring up in other English cities.
An extra 1,700 police officers were deployed in London, where shops were looted and buildings were set alight.
Birmingham, Liverpool, Manchester and Bristol also experienced disturbance.
The prime minister has returned early from his holiday to discuss the unrest, which first flared on Saturday after a peaceful protest in Tottenham over the fatal shooting of a man by police.
At least 334 people have been arrested and 69 charged following the riots across London over the past three days, Scotland Yard has said.
Three people were arrested on Tuesday on suspicion of attempted murder after a police officer was injured by a car in Brent, north west London, while trying to stop suspected looters
In other developments:
- David Cameron will chair the government's emergency committee Cobra to discuss the riots and will also meet Home Secretary Theresa May and Metropolitan Police Acting Commissioner Tim Godwin
- All tube stations in the capital that were closed due to the riots have now re-opened however there is a police cordon at one entrance to Ealing Broadway
- The Tramlink service between East Croydon and Wandle Park has been suspended as a result of the fire at Reeves Corner
- Elsewhere, 100 people have been arrested in Birmingham after scores of youths rampaged through the shopping area, smashing windows and looting from shops
- West Midlands Police also confirmed that a police station in Holyhead Road in Handsworth, Birmingham, was on fire
- There were reports of cars being damaged in Manchester and of up to200 youths with masks roaming through Toxteth in Liverpool
- Police in Bristol said they were dealing with outbreaks of disorder involving about 150 people
Met commander Christine Jones said: "The violence we have seen is simply inexcusable.
"Ordinary people have had their lives turned upside down by this mindless thuggery. The Met will ensure that those responsible will face the consequences of their actions and be arrested."
Monday's violence started in Hackney after a man was stopped and searched by police but nothing was found.
In the first outbreak of violence, groups of people began attacking the police in Hackney at about 16:20 BST, throwing rocks and a bin at officers.
Police cars were smashed by youths armed with wooden poles and metal bars.
Looters also smashed their way into shops, including a JD Sports store, before being dispersed by police.
Nine police forces from other parts of the country assisted in providing support, as well as the City of London Police and British Transport Police.
However, eyewitnesses have reported that as trouble spread across the city, there were often few police officers around when violence flared.