An area off Bora Bora in French Polynesia has been closed off to allow for the destruction of nine shells from the Second World War.
Divers found the shells near the reef passage to the atoll, which for five years was used as a US military base.
Local television said diving experts have been flown in from France and New Caledonia to recover and dispose of the shells.
Shipping is restricted and pleasure craft are being kept at a distance.
Weather conditions permitting, the operation should be completed this week.