Cameron, who was holidaying in Tuscany in central Italy while parts of London burnt, held a meeting of the government's emergency committee after his return here.
There were demands that the army be deployed on the streets of London after three consecutive nights of rioting.
Images of leaping flames across London dealt a blow to its image globally as questions were raised about its ability to hold the 2012 Olympics, now less than a year away.
Riots erupted in Hackney, one of the five boroughs where the Olympics will be held. Home Secretary Theresa May, however, refused to respond to demands that the army be deployed in London, insisting that robust policing will be enough to deal with the situation.
Opposition Labour MP Dianne Abbott favoured curfew to be imposed in London. The police said detention centres in London were full after over 400 arrests over the last three days, and new detainees were being moved to centres outside London.
Trouble spread to Birmingham, Leeds, Bristol and Nottingham.
There was no official word so far about cancellation of the third Test starting tomorrow, but the Indian and English cricket teams have been confined to their hotels in central Birmingham with players tweeting their concern over the developments.
At least two major football fixtures have been cancelled for today. Last night, buildings were torched, shops ransacked and officers attacked with makeshift missiles and petrol bombs as gangs of hooded and masked youths laid waste to streets right across London.
The sheer number of incidents in Hackney, Croydon, Peckham, Lewisham, Clapham and Ealing seemingly overwhelmed the Metropolitan Police at times, who had poured 1,700 extra officers onto the streets.Officers from Thames Valley, Essex, Kent, Surrey and City of London were drafted in to support the Metropolitan Police.
Several buildings were set alight in Croydon, south London, with a massive fire consuming the 100-year-old Reeves furniture store.
The fires were so severe that approach roads into Croydon were thick with smoke leaving some residents struggling to see or breathe.
"Words fail me. It's just gone, it's five generations. My father is distraught at the moment. It's just mindless thuggery," said owner Trevor Reeves.
Tim Godwin, acting Metropolitan Police Commissioner, made a direct appeal to parents to get their children off the streets.
"I do urge now that parents start contacting their children, and ask themselves where their children are," he said.
"There are far too many spectators who are getting in the way of the police operation to tackle criminal thuggery and burglary."The violence first erupted on Saturday in the economically poor north London area of Tottenham after police shot dead a 29-year-old further of four on Thursday. Copycat violence then spread to other areas of London before spreading to districts outside the British capital.