Hundreds of riot police poured into Hackney to try to contain the violence in a district just a few miles (kilometres) from where the 2012 Olympics will take place in a year's time.
As darkness fell, police wielding batons pushed the youths back, while local residents hoping to return to their homes were kept behind police cordons.
In Croydon, an entire block of buildings -- including a 100-year-old family furniture business -- was ablaze, sending raging flames leaping into the night sky.
Just outside of Croydon town centre, hordes of looters roamed the streets unchallenged while the smell of burning cars and buildings hung over the air, an AFP correspondent said.
The violence first erupted on Saturday in the multi-ethnic neighbourhood of Tottenham in north London after a man was shot dead by police two days earlier.
Copycat violence then spread to other areas of the British capital on Sunday before reaching new districts on Monday.
Having resisted calls to cut short his family holiday in Italy amid last week's turmoil on the financial markets, Cameron has decided to return to Britain overnight, his Downing Street office said.
He will chair a meeting of Britain's emergency response committee and hold separate talks with the Home Secretary Theresa May and the acting London police chief on Tuesday.
May, who cut short her holiday, condemned the riots as "sheer criminality" and vowed that the perpetrators would face justice.
"The violence we've seen, the looting we've seen, the thuggery we've seen -- this is sheer criminality," said May, the interior minister.
Police said they had made 215 arrests before Monday's violence, including an 11-year-old boy. At least 35 police officers were injured in the unrest at the weekend.
The violence spread beyond London after police said a group of youths in Birmingham, central England, smashed shop windows in the city centre and stole merchandise.
West Midlands Ambulance Service said 34 patients had been seen by crews for injuries including lacerations, a dislocated knee and general cuts.
Scotland Yard said it had deployed an extra 1,700 officers to deal with the riots.
Earlier, Deputy Prime Minister Nick Clegg on Monday visited homes and businesses burned down during the riots in Tottenham.
Tensions remained high in the area following the shooting on Thursday of 29-year-old Mark Duggan, amid fresh doubts about the original account of his death during a police operation against gun crime within the black community.
The father-of-four was shot in a taxi in what was initially said to have been an exchange of gunfire. But reports said it was possible that police officers were not under attack when they opened fire.
The Independent Police Complaints Commission (IPCC), the watchdog probing Duggan's death, was expected to release the ballistics test results on Tuesday.
On Sunday, shops were looted and police officers pelted with stones in the southern district of Brixton; in Enfield, Walthamstow and Islington in the north and east; and on Oxford Street in the city centre.
Clegg said there was "no excuse whatsoever" for such attacks.
"The violence we saw last night (Sunday) had absolutely nothing to do with the death of Mr Duggan. It was needless, opportunist theft and violence -- nothing more and nothing less," he said.
Although police and politicians said much of the violence was opportunistic, community leaders and many residents in Tottenham said it indicated deep social unease in the area, one of the poorest in London.
"Quite a few people were expecting riots this summer here. The economic situation has been building up and all it needed was a spark," said David Bennie, in his late 40s, who was riding his bicycle up to look at the damage.
Tottenham was the scene of severe rioting on the Broadwater Farm housing estate in 1985 when police constable Keith Blakelock was hacked to death.
After Duggan's death, rumours spread online that he had been killed in an assassination-style execution with shots to the head -- something the IPCC was forced to deny in a statement.
Cheryline Lee, a Tottenham resident in her 50s, told AFP: "The police did not give the community any information about this man who was shot.
"But burning buildings like this is much too much. People have lost their houses and people have lost their jobs as well."
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