Angry youths have burnt cars and confronted police in poor neighbourhoods of the French city of Nantes.
The violence came after police shot dead a young man who had been stopped in his car for a traffic violation.
Police reports say he refused to cooperate with them and then hit one of their officers, lightly injuring him, as he tried to drive off. It was then that he was shot.
The local law courts in Dervalliers neighbourhood were also set on fire.
Police now say they expect more unrest.
Tensions in poor migrant neighbourhoods have frequently escalated into clashes with the police.
In 2005 dozens of cars were torched in similiar unrest in Paris in its outer suburbs where most migrants live.
Nantes' public prosecutor later revealed that the man had been wanted for a year for "organized robbery, concealment and criminal association".
"The police and the justice system need to act independently to clarify what happened this evening," Johanna Rolland, the Mayor of Nantes said.
In a tweet France's Interior Minister Gerard Collomb condemned the unrest and said the police had launched an internal investigation.
Police reinforcements are expected in Nantes, especially in the Breil neighbourhood, which was already on high alert after an incident last week possibly involving a military weapon, according to a source close to the case.