France deployed 45,000 police officers and some armoured vehicles on the streets on Saturday as riots rocked French cities for a fourth night over a teenager's fatal shooting by an officer during a traffic stop.

Buildings and vehicles have been torched and stores looted, and the violence has plunged President Emmanuel Macron into the gravest crisis of his leadership since the Yellow Vest protests that started in 2018.

Unrest has flared nationwide, including in cities such as Marseille, Lyon, Toulouse, Strasbourg and Lille as well as Paris where Nahel M., a 17-year-old of Algerian and Moroccan descent, was shot on Tuesday in the Nanterre suburb.

His death, caught on video, has reignited longstanding complaints by poor and racially mixed urban communities of police violence and racism.

Interior Minister Gerald Darmanin said early on Saturday that 270 people had been arrested on Friday night, bringing the total to more than 1,100 since unrest ignited.

Friday night's arrests included 80 people in the southern city of Marseille, France's second-largest and home to many people of North African descent.

Social media images showed an explosion rocking Marseille's old port area. City authorities said they were investigating the cause but did not believe there were any casualties.

Rioters in central Marseille looted a gun store and stole some hunting rifles but no ammunition, police said. One individual was arrested with a rifle likely from the store, police said. The store was now being guarded by police.

Marseille Mayor Benoit Payan called on the national government to immediately send additional troops. "The scenes of pillaging and violence are unacceptable," he said in a tweet late on Friday.

In Lyon, France's third-largest city, the gendarmes police force deployed armoured personnel carriers and a helicopter to quell the unrest.

Darmanin asked local authorities across France to halt bus and tram traffic from 9pm and said 45,000 officers were being deployed, 5,000 more than on Thursday. (Reuters)