A teenage girl has been killed by a shark as she snorkelled a few metres from the shore on the Indian Ocean island of Reunion.

While the French island has seen occasional attacks on surfers farther out from shore, attacks on swimmers close to shore are rare.

The regional administration for Reunion said the attack occurred in a cove with no lifeguard at Saint-Paul, on the north west of the island. Reunion is east of Madagascar, off the east African coast.

In a statement, the administration said the girl lived on the French mainland but was on holiday on Reunion. She was swimming with another girl who was not harmed.

Authorities warned swimmers to exercise the greatest caution in the area.