* Source says debris likely from a Boeing 777
* Malaysia has sent team to Reunion Island
* Currents could have pushed debris far from crash site - experts
* MH370 disappeared without a trace in March 2014 (Adds detail on ocean currents, comment from China, paragraphs 9, 15-17)
By Tim Hepher and Swati Pandey
PARIS/SYDNEY, July 30 (Reuters) - French authorities are studying a large 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 on Wednesday, 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.
Aviation experts who have seen widely circulated pictures of the debris said it may be a moving wing surface known as a flaperon, situated close to the fuselage.
The piece usually contains markings or part numbers that should allow it to be traced to an individual aircraft, the person familiar with the matter said.
There have been four serious accidents involving Boeing 777s in the 20 years since the widebody jet came into service. 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, about 600 km (370 miles) east of Madagascar, to verify whether the washed-up debris was from MH370. China said it was following developments closely.
The piece 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. Flaperons help pilots control an aircraft while in flight.
"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.
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 said.
Oceanographers said vast, rotating currents sweeping the southern Indian Ocean could have deposited wreckage from MH370 thousands of kilometres from where the plane is thought to have crashed.
If confirmed to be from MH370, experts will try to retrace the debris drift back to where it could have come from. But they caution that the discovery is unlikely to provide any more precise information about the aircraft's final resting place.
"This wreckage has been in the water, if it is MH370, for well over a year so it could have moved so far that it's not going to be that helpful in pinpointing precisely where the aircraft is," Australian Deputy Prime Minister Warren Truss told reporters.
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 MH370, given what was known about Indian Ocean currents.
Malaysia Airlines said it was too early to speculate on the origin of the debris.
The Australian Transport Safety Bureau (ATSB) said it was working with Boeing and other officials.
Boeing declined to comment on the photos, referring questions to investigators.
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 said. (Reporting by Tim Hepher, Emmanuel Jarry and Matthias Blamont in PARIS, Lincoln Feast and Swati Pandey in SYDNEY, Alwyn Scott in NEW YORK, Siva Govindasamy in SINGAPORE and Sui Lee Wee in BEIJING; Writing by Dean Yates; Editing by Alex Richardson and Paul Tait)