Youths battled police for a second night in the Paris suburbs, burning down government buildings and injuring more than 70 officers, forcing tighter security in the troubled towns.
The rioting in six neighbourhoods north of the French capital -- which were also the scene of major unrest in 2005 -- was sparked by the deaths on Sunday of two teenagers whose motorbike collided with a police car in Villiers-le-Bel.
In Villiers, about 100 youths, crouching behind trash cans, hurled objects at 160 riot police who fired rubber bullets and tear gas.
Young rioters in the nearby towns of Sarcelles, Garges-les-Gonesse, Cergy, Ermont and Goussainville were armed with petrol bombs, bottles filled with acid and baseball bats, police said.
The riots lasted about six hours and continued into the early hours of Tuesday.
After the suburban battleground cleared, a helicopter hovered over Villiers, about 20 kilometres (12 miles) north of Paris, looking for potential troublemakers.
Police said Tuesday that of the more than 70 officers injured in the latest clashes five were in critical condition. "One policeman was wounded in the shoulder after being hit by a high-calibre bullet," a security official said.
Some 63 vehicles and five buildings had been torched and a bus, which had no passengers on board, and a truck were set alight in districts near Villiers, police said.
Police said six people were arrested.
Bruno Beschizza of the police union Synergie said the violence was "worse than in the riots of 2005" -- which were also triggered by the deaths of two youths in the northern Paris suburbs.
Officers were "confronted with scenes of real urban guerilla warfare. Things have gone to a new level with the use of weapons including a hunting rifle. Petrol bombs have become the norm, and now we've got this new element to take into account," he said.
"We are getting close to a catastrophe with the use of firearms against police," said another police union UNSA.
President Nicolas Sarkozy, who is in China, has appealed for calm and on Tuesday spoke by telephone to Interior Minister Michele Alliot-Marie, the Elysee palace said.
An initial investigation appeared to confirm the police officers' version that the unlicenced bike smashed into the side of their car during a routine patrol on Sunday. Neither youth was wearing a helmet.
However Omar Sehhouli, brother of one of the victims, accused police of ramming the motorbike and of fleeing the scene.
"This is a failure to assist a person in danger... it is 100-percent a (police) blunder. They know it, and that's why they did not stay at the scene," he told France Info radio.
Sehhouli told AFP the rioting "was not violence but an expression of rage."
Police made nine arrests Sunday as rioters torched a police station, two garages, a petrol pump and two shops, and pillaged the railway station in neighbouring Arnouville. Some 40 police were reported injured.
Police and politicians say the French suburbs remain a "tinderbox" two years after the 2005 riots, which exposed France's failure to integrate its large black and Arab population, the children and grandchildren of immigrants from its African colonies.