"Today, 515 days since the plane disappeared, it is with a heavy heart that I must tell you that an international team of experts have conclusively confirmed that the aircraft debris found on Reunion Island is indeed from MH370," Prime Minister Najib Razak said in an early morning televised address.

The announcement, by providing the first direct evidence that the plane crashed in the ocean, closes a chapter in one of the biggest mysteries in aviation history but still gives families of the 239 victims little clue as to why.

"Although they found something, you know, it's not the end," said Jacquita Gonzales, whose husband Patrick Gomes was a flight attendant on the aircraft.

"They still need to find the whole plane and our spouses as well. We still want them back," she said.

Sara Weeks, the sister of crash victim Paul Weeks, said she was "disgusted" to have been told by a reporter who called her.

"Any time anything happens, it takes you right back to the beginning, the same feelings, same everything, but again this time it has been a week of turmoil and that's going to continue for some time," she told Australia's Fairfax Media.

The airline described the find as "a major breakthrough".

"We expect and hope that there would be more objects to be found which would be able to help resolve this mystery," it said in a statement.

The fragment of wing known as a flaperon was flown to mainland France after being found last week covered in barnacles on a beach on France's Indian Ocean island of Reunion.

Despite the Malaysian confirmation, prosecutors in France stopped short of declaring they were certain, saying only that there was a "very strong presumption".

Paris Prosecutor Serge Mackowiak said this was based on technical data supplied by both the manufacturer and airline but gave no indication that experts had discovered a serial number or unique markings that would put the link beyond doubt.

Boeing representatives confirmed that the flaperon came from a 777 jet, he said, and Malaysia Airlines provided documentation of the actual aircraft used on flight MH370.

"On this basis, it was possible for a connection to be made between the object examined by the experts and the flaperon of the Boeing 777 of MH370," Mackowiak told reporters in Paris.

He said more analysis would be carried out on Thursday, and a fragment of luggage also found in Reunion would be examined by French police as soon as possible.

"A LOT TO BE TOLD"

Investigators looking at the wing flap are likely to start by putting thin slices of metal under a high-powered microscope, to see subtle clues in the metal's crystal structure about how it deformed on impact, said Hans Weber, president of TECOP International, Inc., an aerospace technology consulting firm.

Investigators would probably then clean it and "do a full physical examination, using ultrasonic analysis before they open it up to see if there's any internal damage", Weber said. "That might take quite a while. A month or months."

John Goglia, a former board member of the U.S. National Transportation Safety Board, told Reuters much could be learned from examining the metal and how the brackets that held the flaperon in place had broken.

"From that they can tell the direction and attitude of the airplane when it hit," he said.

However, other experts cautioned that the cause of the disaster may remain beyond the reach of investigators until other debris or data and cockpit voice recorders are recovered.

Greg Waldron, Asia managing editor at industry publication Flightglobal, said the amount of time that has elapsed and the dearth of recovered debris made it harder.

"The real key to finding out what, exactly, happened to MH370 is finding the debris field in the seas west of Australia ... Debris such as the flaperon can only increase our understanding of the last seconds of the flight," he said.

Officials from Malaysia, the United States, Australia, China, Britain, Singapore, and manufacturer Boeing are on hand for the examination at an aeronautical test facility in the French city of Toulouse.

Flight MH370 disappeared on March 8 last year en route from Kuala Lumpur to Beijing. It is believed to have crashed in the southern Indian Ocean, about 3,700 km (2,300 miles) east of Reunion.

Investigators believe that someone may have deliberately switched off the aircraft's transponder, diverted it off course and deliberately crashed into the ocean off Australia.

An initial search of a 60,000 sq km patch of sea floor has been extended to another 60,000 sq km (23,000 sq miles).

"The fact that this wreckage does now very much look like it is from MH370 does seem to confirm that it went down in the Indian Ocean, it does seem very consistent with the search pattern that we've been using for the last few months," Australian Prime Minister Tony Abbott said.