Investigators believe passengers on board Malaysia Airlines flight MH17 could have been conscious for a minute or more as the airliner plummeted to the ground.

The Dutch-led team found the Boeing 777 was brought down by a Buk missile as it flew over heavy fighting in eastern Ukraine, killing all 298 people on board.

Relatives of those on the flight were told their loved ones died almost instantly, according to the findings of the investigation.

Most of those not killed by the missile's impact would have been rendered unconscious by the sudden decompression of the aircraft and a lack of oxygen at 33,000 feet, the board's official report found.

But it also stated: "It cannot be ruled out that some occupants remained conscious for some time during the one to one-and-a-half minutes for which the crash lasted."

One victim was found wearing an oxygen mask, but it was "unclear how the mask got there", the board said.

:: Read the full report here

The front of the jet was partially reconstructed for the release of the key findings in a hangar at Gilze-Rijen military base in The Netherlands.

The Dutch Safety Board found the Buk surface-to-air missile exploded less than a metre from the MH17 cockpit, to the left of the aircraft.

The explosion broke off the front of the plane, it said.

Hundreds of tiny fragments of the missile were discovered in the bodies of the three crew in the cockpit, the board said.

The report also said the plane should never have been flying over eastern Ukraine and that the country should have closed its airspace to civil aviation.

The board said the 61 airlines which continued to fly there should have recognised the potential danger.

Around 160 aircraft used the same route as MH17 on the day of the crash.

:: Key Findings: What We Know Now

"No one considered that civil aircraft at cruising altitude were at risk," Tjibbe Joustra, the head of the Dutch Safety Board, said.

The board recommended international aviation rules be changed to force airlines to be more transparent about their choice of routes.

It also said Russia disagrees with the conclusions of the report, including the type of missile used.

The 15-month investigation was not tasked with apportioning blame or liability for the crash - a separate criminal probe into who is responsible is to follow.

But the Ukrainian and Western governments have long blamed pro-Russian separatists for the crash, claiming they used a Russian-supplied Buk missile.

However, both the Russian and Ukrainian militaries have Buk missile systems in their arsenal.

The state-controlled Russian firm that makes the Buk missile earlier released its own report which contradicted the Dutch findings.