A drug trafficking-related shooting in the western French city of Poitiers escalated into a brawl on Thursday night, potentially involving up to 600 people, French authorities say.

Five people were seriously injured in a drive-by shooting at a restaurant in the city, including a 15-year-old boy who was left in critical condition after being shot in the head, police sources told the AFP news agency.

Interior Minister Bruno Retailleau described the incident as an alarming sign of drug-related violence escalating in the country.

It follows a shooting in the north-western city of Rennes last week which killed a five-year-old boy.

"These shootings are not happening in South America, they are happening in Rennes, in Poitiers, in this part of western France once known for its tranquility," Retailleau told broadcaster BFMTV.

"We are at a tipping point and the choice we have today is a choice between general mobilisation or the Mexicanisation of the country," he said, alluding to Mexico's widespread issues with street crime and violence perpetrated by drug cartels.

The mayor of Poitiers called it "a new episode of violence unacceptable for the neighbourhood".

Shots were fired from a passing car, injuring several young people, police sources said.

Two 16-year-olds were treated for minor wounds.

Pictures from the scene in Place Coimbra, an area of the city known for drug-related crimes, showed the restaurant's facade riddled with bullet holes.

The shooting then triggered fighting between rival gang groups in the area, according to police.

"Tensions between groups broke out, requiring the intervention of the police and the gendarmerie," Vienne regional police said in a statement.

Retailleau said "400 to 600" people were at the scene, though it is not clear how many of those were directly involved.

He was scheduled to visit Rennes, the capital of Brittany, on Friday following the shooting on 26 October, in which a five-year-old boy sitting in a car was shot in the head. Authorities confirmed the shooting was also drug-related.

The drug trade in France has long been viewed as centred in the southern port city of Marseille, where at least 17 drug-related killings have been reported since the start of the year.

But researchers say the influence of drug trafficking in France in recent years has spread beyond the main hubs of Marseille and Paris to medium-sized towns and even rural areas.