The Malaysian government has tabled a 1500-page report on the MH370 mystery, four years after the disappearance of the doomed Malaysian Airlines flight.

The independent investigation report highlighted shortcomings in the government response that exacerbated the mystery.

Dr Kok Soo Chon, investigator in charge of the search, this afternoon told reporters "this is not the final report".

One of the relatives of passengers on board the missing Malaysia Airlines Flight 370 speaks to media after MH370 safety investigation report briefing in Putrajaya, Malaysia. Photo / AP

"This report was not prepared by Malaysia alone," he said at a press conference.

"It is the work of eight countries (including Australia)."

He said the search investigators "have finally reached a consensus" about the final moments of MH370.

"We cannot establish if the aircraft was flown by anyone other than the pilot," he said.

"We can also not exclude the possibility that there's unlawful interference by a third party. And based on the military record, there was no evidence of a rapid change in the altitude or speed to indicate that MH370 was deliberately evading radar.

"We can confirm the turn-back was not because of anomalies in the mechanical system," Dr Soo Chon said.

"We have carried out simulator sessions to determine how the aircraft turned back and we can confirm that the turn-back was made, not under autopilot, but was made under manual control."

Dr Cho Soon said investigators "couldn't find any flaws with the aircraft".

"The weight and balance was normal, within limits the fuel carriage was OK … there was nothing wrong with the aircraft engine health monitor did not register anything, no evidence of unusual engine behaviour," he said.

"There was no airconditioning defects, no pressurisation defects and apparently the autopilot was functioning because the aircraft was flying for 7.5 hours.

"There is no evidence to support the theory that MH370 was taken over by remote control."

Hard copies of the long-awaited and unedited report were distributed to families of those on-board the flight earlier today. Malaysian Transport Minister Anthony Loke said the investigation team also briefed next of kin on the report at the transport ministry.

Those briefed on the contents of the report say investigators "have not assigned blame", Ten News reports.

Sakinab Shah, the sister of the MH370 pilot Zaharie Shah, said the report put to rest the theory that her brother was responsible for the plane's disappearance.

Next of kin looked distraught after receiving the report, many sobbing and saying that the document offered them "no closure", The Guardian reported. Some said that information contained in the report was incorrect. Others reported that while there were no major surprises the report contained more details as to the extent in which Air Traffic Control allegedly "messed up".

MH370 flight Captain Zaharie Ahmad Shah has been a suspect in the plane's disappearance. Photo / Supplied

Earlier, Mr Loke told reporters that "every word recorded by the investigation team (has been) tabled in this report".

"It was tabled fully, without any editing, additions, or redactions," he said.

Grace Nathan, whose mother was on the flight, responded to the release of the report on Facebook. "Just because they call it a final report doesn't mean it's over for the next of kin," she wrote today. "The search must go on. There can be no final report until MH370 is found."

Some very difficult questions being put forth by the NOK to the investigation team. There is a lack of depth in the answers and no adequate answer to some pertinent queries.

Years of investigations have yielded no concrete conclusion as to what downed the plane in March 2014. For more than four years the world has grappled with questions over how the Boeing 777 airliner vanished into thin air en route to Beijing from Kuala Lumpur. Many questions still remain. Was it all just a tragic accident? Were there sinister motives? Was the plane hijacked by somebody? Or was it the captain's doing? But whether we ever find out what really happened to MH370 remains a mystery.

THE MYSTERY OF MH370

In May this year, the country called off a privately-funded underwater search for the aircraft, which became one of the world's greatest aviation mysteries when it vanished with 239 aboard en route to Beijing from Kuala Lumpur on March 8, 2014.

The search led by US-based firm Ocean Infinity covered 112,000 square kilometres in the southern Indian Ocean over three months. It ended with no significant new findings.

Copies of the final investigation report on missing flight MH370 are offered to the media in Putrajaya. Photo / AP

It was the second major search after Australia, China and Malaysia ended a fruitless $200 million search across an area of 120,000 square kilometres last year.

Malaysian Prime Minister Mahathir Mohamad has said the country would consider resuming the search if new clues came to light.

Three wing fragments that washed up on Indian Ocean coasts are so far the only confirmed traces of the Boeing 777 aircraft since it disappeared.

HOW A PLANE VANISHED INTO THIN AIR

The plane left Kuala Lumpur at 12.41am local time on March 8, 2014. Two hundred and thirty nine people were on board, including six Australians.

Around two hours after takeoff, the plane deviated from its planned route to Beijing, veering southwest.

It sent out an automated satellite communication seven and a half hours after takeoff.

Then it disappeared altogether.

An international search followed shortly after, with a total of 26 countries searching the waters off Vietnam for any trace of the missing plane.

On May 5, Malaysia, Australia and China announced their agreement to hold an underwater search, which was led by the Australian Transport Safety Bureau — but there were no answers.

More than a year after the investigation launched, a fragment of the plane's wing was found washed up on Reunion Island, thousands of kilometres from Kuala Lumpur.

But despite on-again-off-again searches spanning from the plane's disappearance up to May this year, it remains a mystery.

THEORIES BEHIND THE PLANE'S DISAPPEARANCE

Experts over the years have offered a number of theories as to what happened to the plane, ranging from a mechanical defect to an intentional murder-suicide by the captain.

Oxygen deficiency: The Malaysian government and the Australian Transport Safety Bureau took the theory that passengers and flight crew — including Captain Zaharie Ahmad Shah — fell unconscious due to an oxygen deficiency. One version of this theory suggests the oxygen supply was deliberately hacked.

Pilot's murder-suicide: In May this year, a team of aviation specialists on 60 Minutes came to the conclusion that Capt Zaharie downed the aircraft in an act of murder-suicide, having plotted a flight plan to nowhere on his home simulator.

Suggested reasons for doing this range from rumours that his marriage was in trouble, to a political protest against then-Malaysian opposition leader Anwar Ibrahim, as a way to destabilise the corrupt government of Najib Razak.

In May this year, a team of aviation experts slammed the murder-suicide theory as "absurd".

Remote takeover: Earlier this year, Malaysia's former Prime Minister Tun Dr Mahathir Mohamad suggested a remote takeover took place to counter a hijacking attempt.

"The capacity to do that is there," he said in March.

"The technology is there. You know how good people are now with operating planes without pilots. Even fighter planes are to be without pilots.

"Some technology we can read in the press but many of military significance is not published."

Chinese terror group: A shadowy group called the Chinese Martyrs' Brigade claimed responsibility for the disappearance of MH370 just days after the plane vanished — but officials were sceptical and said the claim could be a hoax.

The previously unheard of group sent an email to journalists across China that read: "You kill one of our clan, we will kill 100 of you as pay back."

But the message provided no details of what brought the flight down.

Suspicious passengers: In another theory, suspicions fell upon a pair of Iranian nationals who boarded the flight with fake passports.

But authorities concluded it was unlikely that either man had terrorist links or had anything to do with the plane's disappearance.