Looting and riots spread across Britain (Natural Sound)

Violence and looting raged across London and spread to three other major British cities on Tuesday, as authorities struggled to contain the country's most serious unrest since race riots set the capital ablaze in the 1980s.

In London, a third straight night of disorder saw buildings, vehicles and rubbish dumps set alight, stores looted and police officers pelted with bottles and fireworks, as groups of young people rampaged through neighbourhoods.

It was an unwelcome reminder of London's volatility for leaders organising the 2012 Summer Olympics in less than a year.

As authorities struggled to keep pace with unrest unfolding at flashpoints across London, the violence spread to the central city of Birmingham, the western city of Bristol and the northwestern city of Liverpool.

Prime Minister David Cameron cut short his summer holiday in Italy and was headed home for a meeting of the national crisis committee on Tuesday morning.

The riots appeared to have little unifying cause - though some involved in the violence claimed to be motivated by government cuts to public spending.

The government was aiming to toughen its stance against the violence, as some communities complained that stretched police were struggling to contain the unrest with rioters plundering from stores at will, menacing shocked customers at restaurants and attempting to invade homes.

Stores shut early across London, fearful of violence and looting.

Violence first broke out late Saturday in London's northern Tottenham district when a peaceful protest over the fatal police shooting of Mark Duggan, a 29-year-old father of four who was gunned down in disputed circumstances on Thursday, turned violent.

In south London, a massive blaze swept through a 100-year-old family run furniture store in the borough of Croydon and sent thick plumes of smoke into the air, forcing nearby homes to be evacuated.

Police also confirmed they were investigating a nonfatal shooting in Croydon, but were unable to say whether the incident was linked to the chaos.

Dozens of people attacked shops in Birmingham's main retail district, and clashed with police in Liverpool and Bristol - spreading the chaos beyond London for the first time.

In the Hackney area of east London, hundreds of youths attacked shops and set fire to cars, leaving a trail of burning trash and shattered glass.

Police acknowledged on Tuesday that major new bouts of violence had flared in at least five locations, badly stretching their resources.

Many more neighbourhoods saw mobs vandalise commercial streets or break into buildings - some acting with virtual impunity, as authorities struggled to deploy officers to every scene of unrest.