A French judge ordered a manslaughter inquiry on Monday after the death of two teenagers in a crash with police sparked a night of rioting in a flashpoint Paris suburb.

The violence was some of the worst since the nationwide riots in 2005, which erupted in similar circumstances, prompting President Nicolas Sarkozy to appeal for calm.

The two youths, aged 15 and 16, died after their motorbike collided with a police car in the high-immigration suburb of Villiers-le-Bel on Sunday evening. Six hours of clashes followed.

Gangs of youths shot at police, according to one police union, as they torched about 30 cars and looted shops and buildings. Twenty-five police and one firefighter were injured, officials said. Calm was eventually restored just after midnight.

About 100 youths thronged the crash site on a high-rise housing estate, accusing police of fleeing the scene.

Speaking on a trip to Beijing, Sarkozy called for "all sides to calm down and for the judiciary to decide who bears responsibility".

A state prosecutor said she had ordered an internal police investigation for "involuntary manslaughter and failure to assist persons in danger" following the deaths of the two teenagers.

Police said the bike smashed into the side of their car during a routine patrol. Neither youth was wearing a helmet, according to witnesses.

Initial findings by the IGPN police investigatory body appeared to clear the officers of responsibility, according to a police source.

Statements from the officers and witnesses suggested the bike was moving "at very high speed" when it cut across the path of the police car, which was unable to avoid a collision, the source said.

The IGPN also found the officers did not appear to have committed a "serious fault" with regard to their duty to assist the injured, the source said.

But Omar Sehhouli, brother of one of the victims, accused police of ramming the motorbike and of failing to assist the teens.

"This is a failure to assist a person in danger ... it is 100% a [police] blunder. They know it, and that's why they did not stay at the scene," he told France Info radio.

Sehhouli told Agence France-Presse the rioting "was not violence but an expression of rage".

Police made nine arrests as rioters torched a police station, two garages, a petrol pump and two shops, and pillaged the railway station in neighbouring Arnouville.

Officials said there were reports of "small groups attacking shops, passers-by and car drivers" to rob them. One suspect was arrested with jewellery from a looted store.

The police union Alliance offered its condolences to the victims' families, but said it was "unacceptable for a gang of delinquents to use this tragedy as an excuse to set the town on fire".

Police and politicians warn 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.

"These neighbourhoods live in a state of permanent depression, but all it takes is one drop to make the depression boil over into anger," the sociologist Laurent Mucchielli said, although he said a repeat of 2005 was unlikely.

The accidental death of two suburb youths allegedly fleeing police sparked three weeks of nationwide riots in October and November 2005, France's worst social unrest in decades.

Sarkozy, a former interior minister widely reviled in the suburbs for his tough stance on law and order and immigration, has promised a "Marshall Plan" to tackle exclusion and unemployment in the suburbs. Details are to be announced in January.

But the head of the opposition Socialist Party, Francois Hollande, said Sunday's violence was further proof of the "deep social crisis" gripping the French suburbs. -- AFP