SAINT-DENIS, REUNION: Plane debris washed up on the French island of Reunion in the Indian Ocean is almost certainly part of a Boeing 777, a Malaysian official and aviation experts said, potentially the biggest breakthrough in the search for missing Flight MH370.

Malaysian investigators are expected in Reunion on Friday and the object, identified by aviation experts as part of a wing, would then be sent to a French military laboratory near Toulouse for checks, French police sources said.

National carrier Malaysia Airlines was operating a Boeing 777 on the ill-fated flight, which disappeared in March last year en route from Kuala Lumpur to Beijing in one of the most baffling mysteries in aviation history. It was carrying 239 passengers and crew.

The plane piece was found on Wednesday washed up on Reunion, a volcanic island of 850,000 people that is a full part of France, located in the Indian Ocean near Madagascar.

Reunion is roughly 3,700 km (2,300 miles) from the broad expanse of the southern Indian Ocean off Australia where search efforts have focussed, but Malaysian Prime Minister Najib Razak said currents could have carried wreckage that way.

MH370 is believed to be the only 777 to have crashed south of the equator since the jet came into service 20 years ago.

"The location is consistent with the drift analysis provided to the Malaysian investigation team, which showed a route from the southern Indian Ocean to Africa," Najib said.

Aviation experts who have seen widely circulated pictures of the debris, which is about 2-2.5 metres (6.5-8 feet) long, said it may be a moving wing surface known as a flaperon, situated close to the fuselage.

France 2 television showed a picture of the part with the figures "657 BB" stamped on its interior. That corresponds to a code in the 777 manual identifying it as a flaperon and telling workers to place it on the right wing, according to a copy of a Boeing document that appeared on aviation websites.

"It is almost certain that the flaperon is from a Boeing 777 aircraft," Malaysian Deputy Transport Minister Abdul Aziz Kaprawi told Reuters.

Boeing Co (BA.N) has declined to comment on the photos.

NO CHANGE TO SEARCH AREA

Experts have said the bulk of the plane likely sank on impact. The search would continue to focus on the broad section of the Indian Ocean off Australia, a spokesman for Australian Deputy Prime Minister Warren Truss said on Friday.

"That's still the most likely spot and if this piece of wreckage is linked to MH370, then it's entirely consistent, so nothing changes from our end," the spokesman 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 the debris is confirmed to be from MH370, experts will try to retrace its drift back to its source. However, they caution the discovery was unlikely to provide any more precise information about the aircraft's final resting place.

A source close to the French investigation said the plan was to transfer the wing flap to France's European mainland, along with a fragment of luggage that had also been found in the area.

"We're trying to get the debris of wing and the bag fragment sent off as soon as possible, if possible Friday, arriving probably on Saturday," said the source. The wing part would be sent to a military unit near Toulouse, while the luggage fragment may go to a police unit that specialises in DNA tests.

The spokesman for Truss said a preliminary look indicated the luggage had not been in the water for long.

Investigators believe someone may have deliberately switched off MH370's transponder before diverting the plane thousands of miles off course. Most of the passengers were Chinese. Beijing said it was following developments closely.

PAIN FOR FAMILIES

Lingering uncertainty surrounding the fate of the plane has been agony for the families of those on board. Some said the discovery of debris would still not solve the mystery.

"Even if we find out that this piece of debris belongs to MH370, there is no way to prove that our people were with that plane," said Jiang Hui, 41, whose father was on the flight.

Ghyslain Wattrelos, a French businessman whose wife and two children were on the missing flight, told French BFMTV the discovery of the debris had been "extremely painful".

"This doesn't give hope, this is a moment I have been fearing," he said. "As long as there wasn't any evidence of a crash, of wounded, of dead or whatever, there was a little glimmer of hope for us."

Zhang Qihuai, a lawyer representing some of the passengers' families, said a group of around 30 relatives had agreed they would proceed with a lawsuit against the airline if the debris was confirmed to be from MH370.

Daniel Rose, a partner at Kreindler & Kreindler LLP in New York, which is representing more than 50 victims' families, said the discovery was unlikely to trigger a wave of lawsuits.

Families are pursuing a settlement with insurer Allianz (ALVG.DE) through Kreindler, he said, but the firm could sue before a two-year statute of limitations under the Montreal Convention, which governs such accidents, expires in March 2016.