Violence flared again in riot-hit parts of France but the threat of emergency curfews appeared to have taken the edge off the urban unrest that has gripped the country for almost two weeks.

The ritual of car-burnings that has plagued poor city suburbs picked up again after nightfall, but police said there were far fewer incidents pitting rioters against the security forces and no reports of shots fired.

The government Tuesday declared a state of emergency in the worst-hit parts of the country under a decree, applicable from Wednesday, which will allow regional authorities to declare curfews to combat the violence.

The first to act under the new powers, the town of Amiens north of Paris, declared an overnight curfew for unaccompanied under 16-year-olds and a ban on petrol sales to minors, even before the decree comes into force.

Mayors have already declared separate, local curfews, in Orleans and Savigny-sur-Orge, both south of Paris, and in Raincy northeast of the capital.

Across the country, 558 vehicles had been torched at 4:00 am (0300 GMT), compared with 814 at the same time on Tuesday, and 204 people arrested, against 143 the previous night, according to national police figures.

Despite the car-burnings, police said the overall situation was calmer than on recent nights, when dozens of police officers were injured, two by gunshot.

Interior Minister Nicolas Sarkozy, who was visiting police in southwestern Toulouse, a flashpoint of unrest in recent days, said there had been a "fairly significant fall" in the violence.

Earlier, on the outskirts of Toulouse, police charged a gang of youths who had attacked them with stones and firebombs.

A gas-powered bus exploded after it came under attack with a Molotov cocktail in the Bordeaux suburbs, also in the southwest.

In southeastern France, Lyon's entire public transport network was shut down after a Molotov cocktail was thrown at a train station.

And around 50 youths tried, unsuccessfully, to ram their way into a supermarket in the Mediterranean city of Marseille.

In Arras, in northern France, a fire ripped through a shopping centre, spreading from a furniture store to a carpet retailer next door.

The situation was relatively calm in the northeast Paris suburbs where the violence began, police said, with isolated cases of arson and a dozen arrests.

Meanwhile, in neighbouring Belgium, a dozen cars were set alight, although police downplayed concerns about serious violence spreading over the border.

The violence, set off by the deaths of two teenagers on October 27 who were electrocuted in a sub-station where they had hidden from police, spread across the Paris area and in recent days to the rest of the country.

The crisis has thrown into stark relief the failure of French policies for integrating millions of immigrants and their children from its former colonies.

Acknowledging the hardships faced by the Arab community, the government has announced a series of measures to ease access to the job market and stamp out racial discrimination.

PHOTO CAPTION

Policemen patrol in Toulouse, France, after a clash between police and young rioters. (AFP)