New revelations about a missing Malaysia Airlines plane have left anguished relatives contemplating the prospect that those on board endured a terrifying high-altitude hijack ordeal that may have lasted nearly eight hours.

But while the disclosures led to increased speculation of a terror plot or pilot suicide, for some they offered a glimmer of hope -- that flight MH370, carrying 239 passengers and crew, may somehow have landed safely and that their loved ones may still be alive.

For relatives of Bob and Cathy Lawton, a missing Australian couple, the possibility of a terrifying drawn-out fate at thousands of feet reflected their deepest fears.

"That's one of the worst things I could have hoped for," Bob's brother David Lawton told News Limited newspapers.

"Even if they are alive, what did they have to put up with?"

Prime Minister Najib Razak declined to use the word hijack when he briefed the press Saturday, but said new data suggested a "deliberate action" to divert the plane.

The Boeing 777's communications appear to have been switched off manually before the jet veered westward and flew for hours.

What happened during that time remains a mystery. But one report of the plane fluctuating from low to high altitude fuelled fears the passengers may have been well aware they were in terrible danger.

The New York Times said the jet had reached 45,000 feet -- above its approved altitude limit -- before it "descended unevenly to 23,000 feet".

It cited Malaysian military radar signals, but the data has not been confirmed by the authorities.

"At 45,000 feet, it may result in pressurisation problems," said Gerry Soejatman, a Jakarta-based independent aviation analyst.

"But we don't know how the fluctuation went, whether it was gentle or violent and sharp. If it was gentle, only a few sensitive passengers would notice."

- China's fury -

For relatives in China, which had 153 citizens on the flight, the investigators' breakthrough just brought more distress and frustration.

"We are experiencing an ordeal. We are still waiting for (more information)," said one tearful man emerging from a meeting between Malaysia Airlines and relatives in Beijing on Sunday morning.

"We are extremely anxious. A long time has passed and they don't disclose (more) information," he said.

Another branded the meeting "a joke".

"Until they say what really and truly happened, what good is it?" he said.

Malaysian authorities have been severely criticised for failing to share information or for issuing contradictory statements.

China's media made fresh criticism Sunday, saying Malaysia had "squandered" precious time and resources by releasing the dramatic information on the plane's fate a full week after it vanished.

"It is undeniable that the disclosure of such vital information is painfully belated," a scathing editorial by the state-run Xinhua news agency said, noting the "excruciating" seven days it entailed for relatives of the missing.

- Clinging to hope -

Yet for some the new evidence brought relief -- and a reason for hope.

"Our family is relieved that there's an official statement from the Malaysian government, delivered by the Malaysian prime minister, that there's a possibility that the aircraft might have been hijacked," said Indonesian Santi, 42, who goes by one name.

Her brother Sugianto Lo was on the flight with his wife Vinny Chynthya.

"There have been too many speculations about the missing plane so this official statement has helped to quash some of them.

"At least it gives us hope that our loved ones are still safe. We really hope that the various governments will help to look for the plane," she said.

While the theory that the plane landed somewhere and has remained hidden is seen as highly improbable by experts, most do not discount it as impossible.

The multi-nation hunt is now focused on two vast areas, stretching from Kazakhstan to the southern Indian Ocean, with 25 countries searching for the plane.

Malaysian Subramaniam Gurusamy, 60, whose 34-year-old son Puspanathan Gurusamy was on board, refused to believe the worst.

"I am praying every day for divine help. I will not lose hope. I want to hear my son cry out 'Father!" he said.

Selamat Umar, 60, also from Malaysia, placed his faith in his 29-year-old son Khairul Amrison's ability to survive whatever he confronted.

He said the new evidence was "a good sign which shows the plane can be detected and the passengers are safe -- if not all, then some".

"It may be a hijack, but why have there been no demands?" he said.

Although so many questions remain, he is clinging to the belief that his son may one day come home.

"We are definitely worried about his safety but confident that those on the plane will do what they can to survive," said Selamat.

"My son is a Muslim who fasts every Ramadan, so I am sure he has strength."

burs-lm/sm