Four people were killed in western France late Saturday when a Tesla electric car caught fire for reasons not yet determined, prosecutors said Sunday.

The accident occurred outside the city of Niort, causing the deaths of the driver and three passengers who were employees at a restaurant in nearby Melle, according to a source close to police.

"An inquiry has been opened to determine the causes and circumstances of the deadly accident, a probe during which expertise on the vehicle will be requested," a local judge told AFP.

According to preliminary reports, the vehicle rammed into several road signs at high speed.

The passengers on board were already dead when rescuers arrived at the scene, police said. 

Tesla, founded by the billionaire CEO Elon Musk, has frequently faced scrutiny over safety issues.

In April, the carmaker settled with the family of an engineer killed when a Tesla Model X crashed in Silicon Valley in 2018, a move that avoided a trial.

The driver was on a California highway using the Tesla autopilot feature when the car drove into a concrete median, according to the lawsuit.

In December, Tesla recalled more than two million vehicles in the United States and Canada because of risks associated with the autopilot software and a potentially "increased risk of a collision", according to US national regulators.