The two-metre-long piece of wreckage, which seemed to be part of a wing, was found by people cleaning up a beach.
"It was covered in shells, so one would say it had been in the water a long time," said one witness.
French air transport officials have already opened a probe to investigate where the wreckage could have come from.
Xavier Tytelman, an expert in aviation security, said it could not be ruled out that the wreckage belonged to MH370, which vanished without trace in March last year.
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The plane disappeared en route from Kuala Lumpur to Beijing with 239 people on board.
Tytelman noted that local media photos showed "incredible similarities between a #B777 flaperon and the debris found," refering to a Boeing 777 -- the type of plane that disappeared.
He also noted a reference on the wreckage: BB670.
"This code is not a plane's registration number, nor serial number. However... It's clear that this reference would allow a quick identification. In a few days, we will have a definitive answer," Tytelman said.
"We continue to share our technical expertise and analysis. Our goal, along with the entire global aviation industry, continues to be not only to find the airplane, but also to determine what happened -- and why," said the US aviation giant.