French prosecutors have confirmed that a wing part found on a remote Indian Ocean island was from ill-fated Malaysia Airlines flight MH370, a month after tests on the flaperon began.

"It is possible today to say with certainty that the flaperon discovered on Reunion island on July 29 came from flight MH370," Paris prosecutors said in a statement on Thursday, confirming claims made by Malaysia's prime minister last month.

The Boeing 777 disappeared on March 8 last year, inexplicably veering off course en route from Kuala Lumpur to Beijing with 239 people on board, including six Australians.

The disappearance turned into one of the biggest mysteries in the history of aviation, sparking a colossal hunt in the Indian Ocean based on satellite data which hinted at MH370's possible path.

Then at the end of July, a man on Reunion island - a French overseas territory - found the two-metre-long wing part, which was flown to France for tests by aviation experts.

Malaysian Prime Minister Najib Razak was quick to announce that the piece belonged to MH370, but French investigators were more cautious, saying only there was a "very high probability" it came from the plane.

In the statement on Thursday, prosecutors said investigators discovered three numbers on the wing part, and later concluded that one of the figures corresponded to the serial number of an MH370 flaperon.