Police investigators believe high tides may have pushed a decades-old explosive device up to the surface of a beach where a group of ten people had set up camp on the île de Groix, in north western France, radio station France Bleu reports.
The explosion is believed to have taken place in the group’s campfire at around 2am on Sunday morning, after the campers had settled down to sleep for the night.
The 26-year-old victim died on the spot while a 25-year-old friend was taken by air ambulance to hospital in Nantes.
The other eight members of the group, all believed to be in their twenties, were taken to a hospital in Lorient to be treated for shock.
The friends had arrived by boat on Saturday and set up camp in a protected area on the mineral-rich island.
After the incident, police set up a security cordon around the beach. Some twenty police officers joined divers and de-mining squads on the island to determine the cause of death.
Police technicians soon found a metal object they believed was a “piece of ammunition” dating back to World War Two.
Police said the Lorient public prosecutor had also travelled to the island to conduct a manslaughter investigation, which is routine in instances of an unexplained death.