Rioting has spread across London on a third night of violence, with unrest flaring 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, Nottingham and Bristol also saw violence.
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 400 people have been arrested following a wave of what police have described as "copycat criminal activity" across London over the past three days, the Met Police said. More than 69 people have been charged with various offences.
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.
Met Deputy Assistant Commissioner Steven Kavanagh said it was a "shocking and appalling morning for London to wake up to".
"The Met was stretched beyond belief in a way that it has never experienced before," he told BBC Breakfast.
When asked at what stage he would consider bringing in the Army, he responded by saying "all options are being considered".
In other developments:
• David Cameron is chairing 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
• Tube stations in the capital that were closed due to the riots have now re-opened, apart from 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 said a police station in Holyhead Road in Handsworth, Birmingham, was set on fire
• There were reports of cars being damaged in Manchester and of up to 200 youths with masks roaming through Toxteth in Liverpool
• Police in Bristol said they were dealing with outbreaks of disorder involving about 150 people
• Nottinghamshire Police said a police station was attacked in the St Ann's area and 200 tyres were set alight in the street
• "Small pockets of disorder" were dealt with by police in the Chapeltown area of Leeds overnight
Monday's violence started in Hackney after a man was stopped and searched by police but nothing was found.
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 before being dispersed by police.
Nine police forces from other parts of the country have assisted in providing support to the capital city, 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.
