Australian PM Tony Abbott has said the "baffling mystery" of Flight MH370 is closer to being solved, after Malaysia announced that a fragment found in Reunion was part of the missing plane.
PM Najib Razak said experts examining the debris in France had "conclusively confirmed" it was from the aircraft.
However investigators have stopped short of confirming the link, saying only that it is highly likely.
Australia says it remains confident it is searching in the right area.
The Malaysia Airlines plane was travelling from Kuala Lumpur to Beijing on 8 March 2014 when it vanished from radar. It had 239 people on board.
On Thursday, Mr Najib held a news conference in Kuala Lumpur to announce that investigators had "conclusively confirmed that the aircraft debris found on Reunion Island is indeed from MH370".
This would "at least bring certainty to the families", he said.
French prosecutor Serge Mackowiak said only there were "very strong indications" this was the case, and that confirmation would only come after further tests.
The BBC's Hugh Schofield in Paris said Mr Mackowiak's caution did not suggest he had doubts, but that he was exercising legal caution.
Mr Abbott later told reporters that the find "does seem to indicate the plane did come down more or less where we thought it did".
"It suggests that for the first time we may be a little bit closer to solving this baffling mystery," he said.
But he said the Australian-led search for the body of the plane would continue as "we owe it to the hundreds of millions of people who use our skies".
The Australian Transport Safety Bureau (ATSB) has been co-ordinating the deep-sea hunt in the southern Indian Ocean, where the plane is believed to have gone down, thousands of miles from Reunion.
ATSB has said it is possible debris from the plane could have travelled that distance since the crash.
"It is heartening that the discovery of the flaperon is consistent with our search area and we will continue to search this area thoroughly in the expectation we will find the missing aircraft," it said in a statement.
Australia's Deputy Prime Minister Warren Truss said the investigating team was "continuing to finalise its considerations of the wreckage and we will await further detail from them".
Some of the relatives, meanwhile, have expressed frustration with the lack of certainty from officials.
"It's somewhat frustrating," Sara Weeks, whose brother was on the flight, told Fairfax media from New Zealand. "Why not wait and get everybody on the same page so the families don't need to go through this turmoil?"
Most of the passengers were Chinese - many of their relatives have consistently questioned the official view that the plane crashed.
Some gathered in Beijing on Thursday to demand further answers.
"I don't believe this latest information about the plane, they have been lying to us from the beginning," Zhang Yongli, whose daughter was on board, told AFP news agency.
"I know my daughter is out there, but they won't tell us the truth."