Former Austalian prime minister Tony Abbott has revealed the "highest levels" of the Malaysian government believed from "very early on" that the MH370 tragedy was a murder-suicide plot.

Speaking in a new documentary set to air in Australia this week, the former leader, who was PM when the plane disappeared over the South China Sea in 2014, said it was made "crystal clear" to him within a week that the aircraft was almost certainly deliberately downed by the pilot, news.com.au reports.

"My understanding – my very clear understanding – from the very top levels of the Malaysian government is that from very, very early on here they thought it was a murder-suicide by the pilot," Abbott told Sky News' MH370: The Untold Story.

"I'm not going to say who said what to whom. But let me reiterate – I want to be absolutely crystal clear – it was understood at the highest levels that this was almost certainly murder suicide by the pilot.

"A mass murder suicide by the pilot."

Malaysia Airlines flight 370 was carrying 239 people including six Australians and two New Zealanders when it disappeared about 40 minutes into its flight from Kuala Lumpur to Beijing on March 8.

The pilot in command was 53-year-old Zaharie Ahmad Shah, who was one of the airline's most senior captains.

"Good night. Malaysian three-seven-zero," were his last words to air traffic control before the plane dropped off the radar at 1:21am.

Satellite data showed the plane then veered off course, making a series of unscheduled turns over the Strait of Malacca and then out towards the Southern Indian Ocean.

Two formal investigations led by Australia and Malaysia failed to uncover what happened on the flight. The Malaysian government's report said there was no evidence the "competent" Zaharie had hijacked his own aircraft.

But Abbott said officials never mentioned any of the alternative theories, such as a catastrophic fire or terrorist hijacking, to him.

'No reason' to suspect cover up

Critics have claimed the Malaysian government, which owns Malaysia Airlines, tried to cover up the murder-suicide theory to save face.

But Abbott said he had "no reason" to suspect a conspiracy.

"I've read all these stories that the Malaysians allegedly didn't want the murder-suicide theory pursued because they were embarrassed about one of their pilots doing this. I have no reason to accept that," he told Sky News.

Abbott added that if the investigation was somehow misled by the assumption the pilot was innocent, then it should be reopened.

"If it is a fact that the furthest reaches were not explored because of assumptions of a pilot who was no longer at the controls, I would say let's ditch that assumption," he said.

"Let's assume that it was murder-suicide by the pilot, and if there is any part of that ocean that could have been reached on that basis that has not yet been explored, let's get out and explore it."

Last week, a group of leading search experts revealed three new areas that should be investigated.

The search areas represent three different scenarios, with the "highest priority" assuming there was no pilot input after fuel was exhausted.