A piece of debris found on an Indian Ocean island belongs to lost passenger jet MH370, Malaysian prime minister Najib Razak has confirmed.

French, Malaysian, Chinese and American representatives examined the broken fragment, believed to be a wing flap, at a military laboratory in France earlier this week, confirming its link to the missing flight.

“Today, 515 days since the plane disappeared, it is with a very heavy heart that I must tell you that an international team of experts has conclusively confirmed that the aircraft debris found on Reunion Island is indeed from MH370,” Mr Najib told reporters.

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The wing fragment was the first part of the plane located since it went missing last year with 239 passengers and crew on board.

The jet departed at 12:41am on March 8 piloted by Zaharie Shah, 53, and co-pilot Fariq Hamid, 27. One of the two men made final radio contact at 1:19am with the words: “Good night, Malaysian Three Seven Zero”.

In a statement, Malaysian Airlines described the discovery as a “major breakthrough for us in resolving the disappearance”.

Shortly before Mr Najib’s speech, a senior French prosecutor made a slightly more cautious announcement, saying there was a “very high probability” it was from MH370.

His caution was explained by analysts as a need to minimise legal risk, not doubt as to the debris’ authenticity.

Prime Minister Tony Abbott hailed the announcement as vindication of the Australian-led search.

“For the first time we might be a little bit closer to solving this baffling mystery,” he said.

“We have invested upwards of $100 million into this search … we owe it to the 24 million Australians who use our skies.

“We’ll contribute to contribute to the search”

The fragment was found on La Reunion Island, a territory of France in the Indian Ocean near Madagascar.

Questions remain as to why the passenger jet crashed into the sea instead of arriving safely at its intended destination of Beijing.

The ‘flaperon’ from the wing fragment of MH370 is believed to be 2 to 2.5 metres long. Photo: Twitter

Probe for more evidence, answers

Malaysian Airlines was optimistic more debris might be discovered.

“We expect and hope that there would be more objects to be found which would be able to help solve this mystery,” it said in a statement issued as soon as Mr Najib had spoken.

Some relatives of those on board refused to accept the news.

“Now I want to know where the main body of the plane is so that we can take out the passengers and get the black box so we can know what happened,” Jacquita Gonzales said.

“Only that, for us, will be full closure.”

The barnacles, seen attached to the ends of the fragment, could hold more answers as to the flight’s fate. Photo: Twitter

Authorities on the volcanic French island were expected to begin an official search for more debris along the coast.

There were reports French naval ships will be mobilised.

Investigators hope that by examining the barnacles on the wing fragment further, more can be deduced about where the debris had been.

For example, some barnacles could indicate tropical waters, while other types could show it’s been in colder areas.

It also may be possible to learn more about how the plane fragment, and possibly the plane itself, came to be in the water.

Experts can examine if it fell into the ocean due to an on-board explosion in the sky or if it hit the water at a high velocity, as a result of a crash.

Families ‘back to square one’

Rodney and Mary Burrows were on board the flight.

The father of an Australian man on board MH370 said his family was no closer to finding out what happened to their loved one.

George Burrows, the father of Rodney Burrows, said he hoped to get more answers following confirmation of the discovery.

“We were getting over things … and then this happens and [we are] back to square one,” Mr Burrows told ABC radio on Thursday.

Relatives of other victims agreed, saying the finding had reopened old wounds.

“Now I want to know where the main body of the plane is so that we can take out the passengers and get the black box so we can know what happened,” Jacquita Gonzales, the wife of MH370 chief steward Patrick Gomes, told the ABC.

“Only that, for us, will be full closure.”

Some families continued to harbour deep anger and suspicion towards Malaysia’s government.

“I’m still not satisfied,” Lee Khim Fatt, whose wife Foong Wai Yueng was a flight attendant, said.

“There are still so many questions left unanswered, so many holes in the puzzle.

“Until today we have no answers. Don’t just show me a flaperon [wing flap]. Show me more. Answer the questions.”

Relatives of the passengers continued to accuse the airline and Malaysian authorities of bungling the response to the disaster.

Some raised concerns of a possible cover-up and claimed the families of those missing had been treated insensitively.

– with Anthony Colangelo, Jackson Stiles and agencies