Police are on the streets of Tottenham, north London, where overnight riots saw petrol bombs thrown at officers and patrol cars and buildings set alight.
Eight injured police officers were taken in hospital, at least one of them with head injuries.
The unrest began after a protest over the fatal shooting by police of 29-year-old Mark Duggan on Thursday.
About 300 people gathered outside the police station on the High Road after demonstrators demanded “justice”.
London Ambulance Service said a total of 10 people had been treated and nine had been taken to hospital.
Two empty patrol cars were set alight at about 20:20 BST.
Cdr Stephen Watson: “We had no information to suggest that we would have the scale of disorder that now confronts us”
Shops in the area were looted, with people seen pushing away shopping trolleys full of goods. One local resident told the BBC that looting continued beyond daybreak on Sunday.
A double-decker bus was set on fire at the junction of High Road and Brook Street while a shop on the High Road was also set alight.
Fire crews were initially unable to reach the shop due to the disorder but later began tackling the flames.
A BBC TV news crew and satellite truck also came under attack from youths throwing missiles.
The youths had begun attacking another police patrol car before the TV crew were targeted and they were withdrawn in the interests of their own safety. The police car was later set alight.
The BBC’s Andy Moore says the rioters appear to have dispersed on Sunday morning and police were trying to restore calm.
Our correspondent says that since riots in 1985 relations between the local community and police have been generally good, but last week’s shooting raised tension.
He says elements of the community were looking for instant answers but the investigation into Mr Duggan’s death would be more long-term.
‘Calm and normality’
Commander Stephen Watson, of the Metropolitan Police, earlier told BBC News a significant number of officers had been deployed with the aim of restoring “calm and normality to the area as soon as possible”.
Police were continuing to deal with “isolated pockets of criminality” involving a few people, he said in a statement.
Mr Watson said police did not have warnings of last night’s level of disorder, despite being aware of raised tensions after Mr Duggan’s death.
“What we experienced earlier on yesterday evening was a peaceful protest outside Tottenham police station – there was no indication it would deteriorate in this way. For those who involved themselves in this level of violence, there is no excuse.”
Tottenham MP David Lammy appealed for calm on Saturday, saying: “The scenes currently taking place in our community are not representative of the vast majority of people in Tottenham.
“Those who remember the destructive conflicts of the past will be determined not to go back to them.
Tottenham High Road Emergency services remained on Tottenham streets on Sunday morning
“We already have one grieving family in our community and further violence will not heal that pain.
“True justice can only follow a thorough investigation of the facts.
“The Tottenham community and Mark Duggan’s family and friends need to understand what happened on Thursday evening when Mark lost his life. To understand those facts, we must have calm.”
Protesters are believed to have gathered outside the police station at about 17:00 BST.
The force said the situation turned violent when two patrol cars parked about 200 metres away on Forster Road and High Road were attacked.
The spokesman said: “A number of bottles were thrown at these two cars – one was set alight and the second was pushed into the middle of the High Road. It was subsequently set slight.
“The officers were not in the vehicles and were unhurt.”
A friend of Mr Duggan, who gave her name as Niki, 53, said marchers had wanted “justice for the family” and “something had to be done”.
She said some of them lay in the road to make their point. “They’re making their presence known because people are not happy,” she added.
“This guy was not violent. Yes, he was involved in things but he was not an aggressive person. He had never hurt anyone.”
Vanessa Robinson said she had joined the original protest outside the police station and it had begun peacefully.
She said the situation had then turned into “absolute chaos”.
One person at the scene, who gave his name as Tim, said: “It’s an absolute war zone. I walked up there.
“I saw about five youths, all faces covered up. They set a wheelie bin on fire and threw it into the riot police.
“The whole of the police station is surrounded by… about 100 police officers in riot gear and they threw a wheelie bin into it and then started throwing bricks, street signs, anything they could get their hands on, straight at them.”
Another resident, David Akinsanya, 46, said several shop windows had been smashed.
He said: “There was a police line of about 15 riot police sort of in front of the police station on the north side and then there were loads of uniformed officers on the south side of the police station.
“They weren’t making any effort to go into the crowd. Every now and again they would rush the crowd and the crowd would run.
“But there seems to be a lot of anger in Tottenham tonight… as I left they were starting to attack the police station.”
Amateur footage shows clashes between police and protesters near the police station in Tottenham
The Independent Police Complaints Commission is investigating the shooting of Mr Duggan.
A police officer was also injured in the incident, which happened when police stopped a minicab containing Mr Duggan.
IPCC Commissioner Rachel Cerfontyne said: “I understand the distress that the shooting of Mark Duggan has caused to his family and in the community and that people need answers about what happened to him.”
She said the IPCC was in close contact with Mr Duggan’s family, adding: “I have tonight spoken to community representatives and hope to meet with them and others as early as possible.”
A spokesman for Mayor of London Boris Johnson said: “Violence and destruction of property will do nothing to facilitate [the IPCC] investigation and we urge those involved to respect the rule of law.”
40 arrests over Tottenham riots
More than 40 people have been arrested after rioting in Tottenham, north London, saw police attacked and buildings looted during some of the worst violence seen in the capital for years.
Rioters throwing petrol bombs rampaged overnight, setting police patrol cars, buildings and a double-decker bus on fire.
Police said 26 officers were injured as rioters bombarded them with missiles and bottles, looted buildings including banks, shops and council offices, and set alight three patrol cars near Tottenham police station in north London.
London riots: Timeline of violence
People have been left homeless after a night of riots on the streets of Tottenham. Buildings were set alight and shops looted after a peaceful demonstration turned violent. Here is a timeline of what happened.
18:15 BST – Mark Duggan, 29, is shot dead by police at Ferry Lane, Tottenham.
The death occurs during an operation where specialist firearm officers and officers from Operation Trident, the unit which deals with gun crime in the African and Caribbean communities, are attempting to carry out an arrest.
Mr Duggan is a passenger in a minicab and is shot after an apparent exchange of fire. A police officer’s radio is later found to have a bullet lodged in it.
The Independent Police Complaints Commission (IPCC) announces it will investigate the incident and later says it believes two shots were fired by police. It also confirms that an illegal firearm was recovered from the scene.
Before 17:00 – The IPCC provides support to 14 of Mr Duggan’s family members and friends as they formally identify his body.
17:00 BST – Around 300 people gather outside Tottenham police station after marching from Broadwater Farm estate. They say they want “justice” for Mr Duggan and his family.
Officers are forced to close the High Road and put traffic diversions in place. Eyewitnesses report that the protest begins peacefully.
20:20 BST – The violence begins as bottles are thrown at two patrol cars close to the police station. One of the vehicles is set alight, while the other is pushed into the middle of the road before also being torched.
Unconfirmed reports say the incident was sparked off by a confrontation between a teenage protester and a police officer.
Riot officers from the Territorial Support Group and police on horseback are deployed to disperse the crowds but come under attack from bottles, fireworks and other missiles.
20:45 BST – The London Fire Brigade receives its first calls to attend and by 04:30 BST the following morning has dealt with 49 “primary” fires in the Tottenham area and received more than 250 emergency calls from the public.
No firefighters are injured in the disturbances but some are threatened by rioters, according to the London Fire and Emergency Planning Authority.
22:45 BST – As the violence continues, a double-decker bus is burnt out and more petrol bombs being thrown at police and buildings. Shops set alight in the area include an Aldi supermarket and carpet shop.
Looting is reported throughout the night and some thieves take the opportunity to load up car boots and shopping trolleys with stolen goods. Vision Express, Boots, Argos and JD Sports are among the shops affected.
12:00 BST – Fire crews have all the fires under control but are still damping down some burnt-out buildings. Scenes of crime officers begin investigating and gathering evidence.
Police say 26 police officers were injured in the riots and two remain in hospital. Forty-two arrests were made.
Local MP David Lammy tells reporters the community has “had the heart ripped out of it” by “mindless, mindless people”, many of whom he says had come from outside Tottenham to cause trouble.
On the north side of Tottenham High Road on Saturday night, one rioter told the UK’s Channel 4 News that he was “here to tell the police they can’t abuse us, harass us. We won’t put up with it, this is just the beginning, this is war, and this is what you get — fire.”
The BBC reported that its TV news crew and satellite truck came under attack from youths. Sky News also said it was forced to temporarily withdraw camera crews from the area as the situation became increasingly volatile early Sunday.