The announcement was in accordance with international civil aviation rules said Mr Azharuddin, adding the declaration officially ends the search for the missing aircraft and would assist the families of those on board to apply for compensation.
International Civil Aviation rules state the definition of the term "accident" includes "the aircraft is missing" and an aircraft is considered to be missing when the official search has been terminated and no wreckage has been found.
Mr Azharuddin said search international search teams had spared no expense in their search for the plane.
Every credible lead had been pursued and all available data that tracked the plane to a corner of the southern Indian Ocean had been reviewed, he said.
But Sarah Bajc, whose partner Philip Wood was on board the plane, rejectected the announcement.
"I think they are lying," she said. "It could very well be that the plane crashed. But there is no evidence, and until there is evidence we just can't believe them," she said, referring to the Malaysian government and airline.
"It is impossible to bring any closure until we have proof."
Some relatives accuse the Malaysian government and the airline of a chaotic response to the plane's initial diversion, which allowed it to disappear, and a subsequent cover-up; charges Kuala Lumpur and Malaysia Airlines strenuously deny.
Flight MH370 vanished on Saturday March 8 2014 during a flight from Kuala Lumpur to Beijing in China and no trace of the plane, passengers or crew has been found despite extensive searches.