FRANKFURT (Reuters) - Tesla Motors <TSLA.O> is cooperating with French local authorities investigating a fire involving one of its Model S cars during a test drive in Biarritz, it said on Tuesday.

"We are working with the authorities to establish the facts of the incident and offer our full cooperation. The passengers are all unharmed," a Tesla spokesman said, adding that passengers were able to get out of the car, a Model S 90 D, safely before the fire.

The incident happened during a test drive event organized by Tesla in France, the spokesman said.

In 2013, Tesla's shares fell sharply after images emerged of a Model S catching fire after a driver struck a large metal object that punctured a cover protecting the lithium-ion battery.

Lithium-ion batteries are vulnerable to catching fire if damaged.

Overall the Model S is seen as a safe vehicle. It has won a five-star safety rating from the U.S. National Highway Traffic Safety Administration in every testing category. The Model S also has the highest rating given by influential magazine Consumer Reports, with a score of 99 out of 100 points.

(Reporting by Edward Taylor and Tina Bellon; editing by Susan Thomas)