The British capital saw a night of relative calm, with 16,000 police patrolling the streets. But rioting spread to new areas of the country as the worst unrest England has seen in a generation persisted for a fourth consecutive night.

Police in the central city of Nottingham said that a group of between 30 and 40 men firebombed a police station in the city centre Tuesday night. There were no reports of injuries, and several male suspects were attested nearby.

Seven people were arrested in the northwestern city of Manchester after hundreds of youths ran amok, setting fire to a clothing store downtown and a library in nearby Salford.

About 200 rioters also clashed with police in Liverpool on Tuesday night, The Guardian newspaper reported. And there were minor clashes with police in the central communities of Leicester, Wolverhampton and West Bromwich.

Meanwhile an eerie calm settled over London, where police had pledged to nearly triple their presence on the streets in a bid to head off another night of rioting, which has claimed at least one life.

While British police generally avoid tear gas, water cannons or other strong-arm riot measures, police in London said Tuesday that plastic bullets could be used to stop looting if it persists.

Authorities have been scrambling to gain control over the marauding crowds of largely poor, diverse youths. At least 685 people had been arrested and 111 charged as of Tuesday night, Scotland Yard said.

The rioting began Saturday night at a vigil held in the gritty London neighbourhood of Tottenham for a dark-skinned man shot and killed by police under suspicious circumstances.

By Tuesday night some London residents reportedly took to the streets in order to help defend their neighbourhood, and the leader of a far-right group called the English Defence League said 1,000 of its members would patrol areas that have suffered rioting.

The recurring violence prompted British Prime Minister David Cameron to cut short his family vacation and return to London overnight Monday, so that he could deal with what he described as "sickening" riots.

After holding an emergency meeting Tuesday, Cameron refrained from calling in the military, but said the British public should be assured that the government will not allow the destructive rioting to continue.

"People should be in no doubt that we will do everything necessary to restore order to Britain's streets and to make them safe for the law-abiding," Cameron told reporters.

Instead, Cameron recalled lawmakers from their summer recess so they can discuss the crisis later this week.

The prime minister promised that the perpetrators will "feel the full force of the law" and will be prosecuted accordingly.

News of the first riot-related death emerged Tuesday when the BBC reported that a 26-year-old Croydon man died hours after he was found in his car suffering from gunshot wounds. A murder inquiry is now underway into the victim's death.

Since the weekend, the riots have spread to other British cities, including Birmingham, Liverpool and Bristol.

But it is in London where residents have seen cars and buildings burned, shops looted and young hoodlums running amok with impunity for three straight nights.

Police said 111 officers, five police dogs and 14 citizens were hurt over the three days, including a man in his 60s who sustained life-threatening injuries at the hands of looters after he tried to put out a fire they had set in the west-London neighbourhood of Ealing.

In Croydon, Graham Reeves saw his family's 140-year-old department store gutted by a fire started during the riots.

"No one's stolen anything. They just burned it down," he said. "It's pointless."

Simon Dance, 27, said he and his wife were frightened enough by what they saw in their north London neighbourhood of Camden to prepare for the possibility that they might have to leave their home.

"We locked all the doors, and my wife even packed a bag to flee. We had Twitter rolling until midnight just to keep up with the news. We were too afraid to even look out the window," Dance told The Associated Press.

CTV's London Bureau Chief Tom Kennedy said the British public has been shocked by the violence that the rioters have unleashed on the streets.

"The dilemma that this country is having is explaining how on Earth are there so many disaffected youths who feel comfortable with going out into the streets and committing these dreadful acts of violence -- thievery, looting and burning people out of their homes, which was also happening," he said.

"So I think there's a real bewilderment in this country now, how on Earth it came to this."

Andrew Silke, the head of criminology at the University of East London, said the public is also angry about the inability of police to quickly bring the riots to an end.

"The public wanted to see tough action. They wanted to see it sooner and there is a degree of frustration," Silke told The Associated Press in an interview.

The rioters do not appear to have a single unifying cause that has drawn them to the streets night after night, but some suggested they are acting out in protest of cuts to welfare and the public sector, while others say a distrust of the police is to blame.

"This is the uprising of the working class. We're redistributing the wealth," a 28-year-old man and self-described anarchist named Bryn Phillips told The Associated Press.

Others are convinced that the people involved with the riots are simply looking for an opportunity to break the law.

"It's just an excuse for the young ones to come and rob shops," said Brixton resident Marilyn Moseley.

With files from The Associated Press