Distrust, disbelief, despair: two years after their loved ones vanished, many Chinese relatives of those on board Malaysia Airlines flight MH370 still refuse to believe they are somewhere at the bottom of the Indian Ocean.

The unique circumstances of the disaster -- including conflicting initial accounts, an inconclusive search and a backdrop of scepticism all contribute to their insistence, specialists say.

For many Chinese families, the impact of the disaster was magnified by the one-child policy, which over the past 30 years forced hundreds of millions of parents to pin all their hopes for the future on a single offspring.

Without that hope, one mother said, she "might as well be dead".

But with a two-year deadline to take legal action looming, scores have filed suit for the wrongful deaths of their relatives, even while some insist they are still alive.

In the US, 43 passengers' relatives have sued in New York, and, among other legal actions, on Monday the families of 12 Chinese passengers filed cases against the airline, aircraft manufacturer Boeing, aero-engine maker Rolls Royce and insurers at a Beijing court.

Many of the parents of MH370's 153 Chinese passengers -- among 239 people on board -- are elderly and retired, a time when their children would traditionally have looked after them in a multi-generational household.

"Because of China's special circumstances, I was only allowed to have one son," said Lin Xiaolan, 51.

"When something like this happens, how can you talk about compensation, settling differences? How can you possibly settle this?"

A gynaecologist from Xining, in the northwestern province of Qinghai, she says she has a "mother's sixth sense" that her son Lin Annan, 27 at the time, is still alive.

"As mothers, none of us can live normal lives anymore, because there has been no answer to the mystery -- it's always hanging there, this knot of worry in your heart," she said.

Malaysia Airlines was involved in a cover up that was probably a "political game between nations", she said.

"If we don't file suit, it's equivalent to giving up the right to look for our children. The goal of the lawsuit isn't to get money, but to seek justice for our children and the truth."

- Conspiracy theories -

An initial search for the aircraft focused on the South China Sea, before radar traces showed it turning back to cross peninsular Malaysia and over the Indian Ocean. Citing imprecise satellite data, authorities believe it flew south for hours before going down in one of the remotest locations on earth.

A vast Australian-led search of 120,000 square kilometres (46,000 square miles) of seabed has so far failed to locate the wreckage, with only a piece of the plane washing up on the Indian Ocean island of Reunion as solid evidence of its fate.

Conspiracy theories offered relatives a way to try to address the fact that "you do feel powerless, you don't know what's happened, and you're looking for ways to explain it," said Karen Douglas, professor of social psychology at the University of Kent in Britain, who has used MH370 in her research in the field.

Authoritarian governments whose pronouncements are not believed by their citizens could create more fertile ground for such beliefs, she told AFP.

"It makes perfect sense that in a place where you're forced into a corner and you don't really trust, then it's likely that conspiracy theories might be more plausible."

- 'Sold out' -

Gao Xianying, 65, who lost her daughter, son-in-law, and three-year-old granddaughter on the flight, moved from Anhui to Beijing so that she can protest daily at the offices of Malaysia Airlines, the Malaysian and US embassies, and China's foreign ministry.

"For days on end I'll dream the same dream - that my daughter has come home and is calling me 'mother'," she said, crying.

"I used to be so happy, my old age was the happiest time of my life -- I raised my daughter well and got her married. But now my whole life has been upended; I'm living, but I might as well be dead."

Many of the passengers on board MH370 were their family's primary breadwinners, leaving their families in straitened circumstances.

Wen Wancheng, 65, a retired sewage collector whose 35-year-old son was on board, has borrowed to support his daughter-in-law and two grand-children, aged three and nine.

"My son hasn't come home and his children are so young. One of the hardest things has been the financial pressure."

According to lawyers, Malaysia Airlines offered Chinese families compensation of 2.52 million yuan ($386,000) per victim.

Malaysia Airlines said in February that 42 next-of-kin of those on board had collected "full compensation", without giving further details.

Wen looked on those who had taken the money with scorn. "You've basically sold out your child. You're no better than a thief."