A protester died on Wednesday as police clashed with demonstrators in Mayotte, a French island in the Indian Ocean that has been paralysed for three weeks by social unrest.

Local police said the 39-year-old man, Ali El Anziz, apparently died of a heart attack while taking part in demonstrations against soaring food prices. An autopsy would be conducted to confirm the suspicion, police said.

His death came as police and protesters clashed in the capital Mamoudzou following weeks of demonstrations.

"The police... were targeted by thrown stones," Mayotte prefect Thomas Degos said.

"They responded using tear gas grenades and flashballs," he said, referring to a non-lethal firearm developed for riot police in France. "During the clashes a protester collapsed unconscious on the ground."

He said medical workers were unable to revive Anziz and he was declared dead in hospital. "The doctors who examined him found no trace of any impact on his body," Degos said.

Discontent over food and fuel prices led to a strike organised by the local branches of France's top unions which has all but paralysed the tiny island for three weeks.

Mayotte has a population of around 200,000 and is part of the Comoros archipelago in the southwestern Indian Ocean, between Madagascar and Mozambique.

In 1974, the other three islands in the archipelago acquired their independence from France as the Comoros but Mayotte became a French "collectivity".

On April 1 this year, Mayotte became a full-fledged French department, with full voting and citizenship rights.