Rampant looting and raging fires engulfed swaths of London on Monday as the wave of civil unrest that has gripped this sprawling capital escalated sharply, including riots in a neighborhood not far from that of the athletes’ village and shiny stadiums being built for the 2012 Olympic Games.

The images of violence — with hundreds of youths looting shops, setting businesses ablaze and clashing with police in almost a dozen neighborhoods — deeply shocked Londoners, dealing the city an enormously damaging blow less than a year before the start of the Olympics.

Police called in hundreds of reinforcements and volunteer officers, but were struggling to keep pace with the clashes.

In the worst bout of urban violence to hit Britain in more than two decades, parts of London morphed into lawless no man’s lands. Most of a block in the Croydon neighborhood erupted Monday night into an inferno that incinerated the 140-year-old Reeves furniture store, a south London landmark. After midnight Tuesday, an even larger fire tore through a Sony distribution center on the other side of the city, in Enfield.

Gangs of youths roamed one south London neighborhood while carrying molotov cocktails, the BBC reported. And widespread looting was reported in the west London borough of Ealing after a shopping mall caught fire.

The violence spread beyond the capital, to Birmingham, the country’s second-largest city, as well as Liverpool, Bristol, Leeds and Nottingham.

Prime Minister David Cameron cut short a vacation to Italy and was returning to London overnight to chair an emergency cabinet meeting to handle the mounting crisis. Overwhelmed by the scope of the violence, the embattled Metropolitan Police called in reinforcements from police forces outside London.

“Nobody should go out on the streets unless they have business to do so,” Simon Hughes, a national lawmaker from an inner London neighborhood, told reporters.

The increasing unrest — spreading in part via BlackBerry text messages as well as postings on Twitter and other social networking sites — was taking root mostly in the powder keg of poorer neighborhoods and away from the iconic central heart of London popular with foreign vacationers. But there were outbreaks of severe violence in even gentrified neighborhoods such as Clapham, as well as reports that 50 youths had vandalized shops in the famous shopping district of Oxford Circus.

Police said 250 people had been arrested over the past three days, and at least 69 people have been charged with offenses, the Associated Press said.

Three people were arrested on suspicion of attempted murder of a police officer who was struck by a car in north London early Tuesday, AP said.

The violence first erupted Saturday night in Tottenham, a gritty north London neighborhood, after the fatal shooting of a black resident by police investigating gun crimes. Those riots set off a ripple effect among disenfranchised youths in other parts of the city Sunday, and the unrest increased in size and intensity Monday.

Some, including former London mayor Ken Livingstone, suggested that the Tottenham riot was an unleashing of pent-up resentment over the weak economy, high unemployment rates and historically deep budget cuts that are decreasing government funding for poor communities and grass-roots charities. He blamed a sense that young Britons are facing “the bleakest future.”

“This is the first generation since the Great Depression that have doubts about their future,” he told the BBC.

But others — including Britain’s coalition government — denounced the spreading riots as an extraordinary rampage of opportunistic criminality after the Tottenham unrest. Unlike the protests by anarchists in December that included vandalism of central London businesses, those participating in riots in the past 48 hours showed no signs of trying to make a political statement.

The unrest left residents and shopkeepers in parts of the city barring their doors or leaving besieged neighborhoods. In Hackney, a neighborhood not far from the new Olympic Park, which has become a showcase for a city trying to turn the Games into an opportunity for urban redevelopment, riots erupted in the late afternoon. A line of police officers with plastic shields cordoned off a commercial artery that had effectively been taken over by masked looters, who broke shop windows and seemed to steal indiscriminately.

“The crimes are being committed, and the police are just standing by,” said Andrew Faris, director of Rhythms of Life International, a homeless shelter near the center of the Hackney riots. “People are scared. There are angry young people doing whatever they want. How can this be happening next door to the Olympic site?”

The unrest in Hackney, which seemed to start the rapid spread of violence Monday, began in the late afternoon, reportedly after police stopped and searched a young man.

Police officials said they were deploying extra officers to the streets, but their restraint — television images showed them watching from a distance as looters made away with merchandise — gave rise to sharp criticism from some quarters. Officials said they had arrested 334 people and charged 69. The ages of those arrested ranged from 11 to 49, although most were in their teens and 20s.

Scotland Yard Deputy Assistant Commissioner Stephen Kavanagh told reporters that the force had deployed “significant resources” on the streets but did not disclose the actual number of officers. Police threatened to arrest those spreading messages inciting violence on Twitter and other social networking sites.

“When we have large numbers of criminals intent on that type of violence, we can only do that — get lots of officers there quickly and try to protect local businesses and local people,” Kavanagh said.

British Home Secretary Theresa May, the cabinet minister in charge of the police, publicly defended the force, saying law enforcement authorities were doing everything they could.

May rejected assertions that the youths had any political motivation. “There is no excuse for violence, there is no excuse for looters, there is no excuse for thuggery on our streets,” she said. “And those responsible will be brought to justice.”