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.

Call for more troops

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.

Three police officers were slightly wounded early on Saturday. A police helicopter flew overhead.

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 9 p.m. (1900 GMT) and said 45,000 officers were being deployed, 5,000 more than on Thursday.

"The next hours will be decisive and I know I can count on your flawless efforts," he wrote to firefighters and police officers.

Asked on TF1's main evening television news programme whether the government could declare a state of emergency, Darmanin said: "Quite simply, we're not ruling out any hypothesis and we'll see after tonight what the President of the Republic chooses."

In Paris, police cleared protesters from the iconic central Place de la Concorde square on Friday night after an impromptu demonstration.

More than 200 police officers have been injured since the unrest erupted and hundreds of rioters and have been arrested, Darmanin said, adding their average age was 17.

Macron earlier urged parents to keep children off the streets.

Players from the national French soccer team issued a rare statement calling for calm. "Violence must stop to leave way for mourning, dialogue and reconstruction," they said, in a statement posted on star Kylian Mbappe's Instagram account.

Looters have ransacked dozens of shops and torched some 2,000 vehicles since the riots started.

Events including two concerts at the Stade de France on the outskirts of the capital were cancelled. Tour de France organisers said they were ready to adapt to any situation when the bicycle race enters the country on Monday after starting in the Spanish city of Bilbao.

Macron has crisis meeting

Macron left a European Union summit in Brussels early to attend a second cabinet crisis meeting in two days. He has asked social media to remove "the most sensitive" footage of rioting and to disclose identities of users fomenting violence.

Darmanin met representatives from Meta, Twitter, Snapchat and TikTok. Snapchat said it had zero tolerance for content that promoted violence. A friend of the victim's family, Mohamed Jakoubi, who watched Nahel grow up, said the rage was fuelled by a sense of injustice after incidents of police violence against minority ethnic communities, many from former French colonies.

"We are fed up, we are French too. We are against violence, we are not scum," he said.

Macron denies there is systemic racism inside law enforcement agencies. Videos on social media showed urban landscapes ablaze. A tram was set alight in the eastern city of Lyon and 12 buses gutted in a depot in Aubervilliers, northern Paris.

Some tourists were worried, others supportive of protesters.

"Racism and problems with the police and minorities is an important topic going on and it's important to address it," U.S. tourist Enzo Santo Domingo said in Paris.

Some Western governments warned citizens to be cautious.

In Geneva, the U.N. rights office emphasised the importance of peaceful assembly and urged French authorities to ensure that use of force by police was non-discriminatory.

"This is a moment for the country to seriously address the deep issues of racism and racial discrimination in law enforcement," spokesperson Ravina Shamdasani said.

The policeman whom prosecutors say acknowledged firing a lethal shot at the teenager is in preventive custody under formal investigation for voluntary homicide - equivalent to being charged under Anglo-Saxon jurisdictions.

His lawyer, Laurent-Franck Lienard, said his client had aimed at the driver's leg but was bumped when the car took off, causing him to shoot towards his chest. "Obviously (the officer) didn't want to kill the driver," Lienard said on BFM TV.

The unrest has revived memories of three weeks of nationwide riots in 2005 that forced then President Jacques Chirac to declare a state of emergency following the death of two young men electrocuted in a power substation as they hid from police.