Paris: France said on Friday the coming hours would be decisive after three nights of riots since a police officer shot dead a teenager at a traffic stop in a working class suburb of Paris.

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 ignited longstanding complaints among poor, racially mixed, urban communities of police violence and racism.

"The next hours will be decisive and I know I can count on your flawless efforts," Interior Minister Gerald Darmanin wrote to firefighters and police officers seeking to quell unrest that has been breaking out after nightfall.

He asked local authorities to halt bus and tram traffic from 9 p.m. (1900 GMT) across the whole of France. The government has said all options would be considered to stop the unrest.

With some 40,000 police officers deployed, more than 200 of them were injured and 875 people arrested overnight into Friday, authorities said. Buildings and vehicles were torched, and stores looted.

While so far the worst of the violence has been confined to city suburbs, any sign it is spreading into the centres of France's biggest cities would mark a significant escalation.

Already looters have ransacked shops including an Apple store in the eastern city of Strasbourg on Friday, a local official said. A source told Reuters that several Casino supermarkets had been looted.

In the Chatelet Les Halles shopping mall in central Paris, a Nike shoe store was broken into, and several people were arrested after store windows were smashed along the adjacent Rue de Rivoli shopping street, police said.

Events including two nights of concerts by a French singer at the Stade de France on the outskirts of Paris have been cancelled. Tour de France organisers say they are ready to adapt to any situation when the race enters the country on Monday after starting in the Spanish city of Bilbao.

In the southern city of Marseille, France's second largest, authorities banned demonstrations set for Friday, and encouraged restaurants to close outdoor areas early. They said public transport would stop at 7 p.m.

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.

For Mohamed Jakoubi, who watched Nahel grow up as a child, the rage was fuelled by a sense of injustice in the banlieues 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.

FLASHPOINT NANTERRE
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.

In Nanterre on the capital's outskirts, protesters torched cars, barricaded streets and hurled projectiles at police following an earlier peaceful vigil.

The energy minister said several staff of power distribution firm Enedis were injured by stones during clashes. The interior ministry said 79 police posts were attacked overnight, as well as 119 public buildings including 34 town halls and 28 schools.

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," American tourist Enzo Santo Domingo said in Paris.

Some Western governments warned citizens to be cautious.

In Geneva, the United Nations 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 down towards the driver's leg but was bumped, 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.

That wave of violence erupted in the Paris suburb of Clichy-sous-Bois following the death of two young men electrocuted in a power substation as they hid from police.