Malaysian authorities and the airline had until now refrained from drawing firm conclusions about the fate of the plane and its 239 passengers and crew, as many desperate next-of-kin continue to insist it may have landed safely somewhere.
But Thursday's declaration that MH370 was an "accident" was essentially a formal announcement that the plane had indeed crashed somewhere after its disappearance on March 8 and that all aboard had perished.
"It is therefore, with the heaviest heart and deepest sorrow that, on behalf of the government of Malaysia, we officially declare Malaysia Airlines flight MH370 an accident," civil aviation chief Azharuddin Abdul Rahman said in a televised announcement.
"All 239 of the passengers and crew on board MH370 are presumed to have lost their lives," he added.
Urging relatives to move forward, he said it was "important that families try to resume normal lives".
Malaysia Airlines later said it would begin contacting families to proceed with a "fair and reasonable" compensation process.
But Sarah Bajc, whose partner Philip Wood was on board the plane, was one of several relatives who poured scorn on the announcement.