* Source says debris likely from a Boeing 777
* Malaysia has sent team to Reunion Island
* Currents could have pushed debris far from crash site - expert
* MH370 disappeared without a trace in March 2014 (Adds more reaction)
By Tim Hepher and Lincoln Feast
PARIS/SYDNEY, July 30 (Reuters) - French authorities are studying a piece of plane debris found on Reunion Island in the Indian Ocean to determine whether it came from Malaysia Airlines Flight MH370, which vanished last year in one of the biggest mysteries in aviation history.
A person familiar with the matter told Reuters the part was almost certainly from a Boeing 777, the type of aircraft operated by Malaysia Airlines on the ill-fated flight, but that it had not yet been established if it was a piece of the missing plane.
France's BEA air crash investigation agency said it was examining the debris, found washed up on the French island east of Madagascar, in coordination with Malaysian and Australian authorities, but that it was too early to draw conclusions.
Nevertheless, the discovery could be the biggest breakthrough in the so far fruitless search for MH370, which disappeared without a trace in March 2014 carrying 239 passengers and crew while en route from Kuala Lumpur to Beijing. Most of the passengers were Chinese.
There have been four serious accidents involving 777s. Only MH370 is thought to have crashed south of the equator.
Investigators believe someone deliberately switched off the plane's transponder before diverting it thousands of miles off course. Search efforts led by Australia have focused on a broad expanse of the southern Indian Ocean off Australia, roughly 3,700 km (2,300 miles) from Reunion Island.
Malaysia said it had sent a team to Reunion to verify whether the washed-up debris was from MH370. The island, about 600 km (370 miles) east of Madagascar, is a French Indian Ocean territory.
"The part has not yet been identified and it is not possible at this hour to ascertain whether the part is from a B777 and/or from MH370," a BEA spokesman said in an email on Wednesday.
The plane part, which according to aviation experts may be a moving wing surface known as a "flaperon" situated close to the fuselage, usually contains markings or part numbers that should allow it to be traced to an individual aircraft, the person familiar with the matter said.
Greg Feith, an aviation safety consultant and former crash investigator at the U.S. National Transportation Safety Board (NTSB), said his sources at Boeing had told him the piece was from a 777.
Whether it was MH370 was not clear, he said.
"But we haven't lost any other 777s in that part of the world," Feith added.
Robin Robertson, an oceanographer at the University of New South Wales in Sydney, said the timing and location of the debris made it "very plausible" that it came from the wreckage of MH370, given what was known about Indian Ocean currents.
"It's about the right time for something. It depends on where it went in, but it's about the right time for debris to wash up," Robertson said.
Malaysia Airlines said it was too early to speculate on the origin of the debris.
The part is roughly 2-2.5 metres (6.5-8 ft) in length, according to photographs. It appeared fairly intact and did not have visible burn marks or signs of impact.
"In the event that the wreckage is identified as being from MH370 on La Reunion Island, it would be consistent with other analysis and modelling that the resting place of the aircraft is in the southern Indian Ocean," Australian Deputy Prime Minister Warren Truss said in a statement.
The Australian Transport Safety Bureau (ATSB) said it was working with Boeing and other officials.
"We know about it and we are trying to work with our French colleagues to try and figure out if this is from MH370. It could take some time," Chief Commissioner Martin Dolan told Reuters.
Boeing declined to comment on the photos, referring questions to investigators.
A spokeswoman for the Federal Aviation Administration (FAA) declined to comment, saying the investigation was ongoing.
John Goglia, a former NTSB member, said the search area for MH370 might need to be greatly expanded.
"It could still be a vast area," he said, because the piece could have floated a long distance. "It might move the search area further west."
Aviation consultant Feith said that if the part was from MH370, the bulk of the plane likely sank, while the flaperon had air pockets that allowed it to float below the water's surface.
Finding the wreckage would involve reverse engineering the ocean currents over 18 months, Feith said. "It's going to take a lot of math and science to figure that out," he added. (Reporting by Tim Hepher, Emmanuel Jarry and Matthias Blamont in PARIS, Lincoln Feast and Swati Pandey in SYDNEY, Alwyn Scott in NEW YORK and Siva Govindasamy in SINGAPORE; Writing by Dean Yates; Editing by Toni Reinhold and Alex Richardson)