A Frenchman earlier this year discovered a gold treasure worth $800 000 (R16.8 million) while digging a swimming pool in his garden, local officials have said.

The man informed the local authorities after he made the discovery in May, and they allowed him to keep the gold as it did not come from an archeological site, the council in the eastern town of Neuville-sur-Saone said on Wednesday.

He found "five gold bars and many coins" buried in plastic bags, local newspaper Le Progres reported.

Police found the gold had been acquired legally and had been melted down some "15 or 20 years ago" at a nearby refinery, it said.

The previous owner of the garden has died, the town hall said, and how the gold ended up there remains a mystery.