France's air and sea search for wreckage from Malaysia Airlines Flight MH370 off the coast of Reunion island is being scaled back because no new debris has been discovered in days.

Aeroplanes, helicopters and ships were deployed to scour a 10,000-square-kilometre area of the waters surrounding the French territory in the eastern Indian Ocean after a wing fragment believed to have come from the Boeing 777 washed ashore in late July.

Malaysia's prime minister said the object "conclusively" come from the jet, but officials in France said only that there were strong indications it matched the missing plane.

The prefecture on Reunion Island said it would continue to be vigilant for further wreckage.

The plane disappeared without a trace with 239 people aboard about an hour after it left Kuala Lumpur en route to Beijing on March 8, 2014.

The plane mysteriously changed course and went out over the Indian Ocean before losing all contact.

Experts believe the plane went down in the waters off the western coast of Australia.