Malaysia's government pledged Monday it "will not rest" until missing flight MH370 is found but relatives said on the 100th day since the plane's disappearance that they wanted answers, not more promises.

The Malaysia Airlines flight disappeared on March 8 with 239 passengers and crew, shocking the world and shattering families of those aboard, who still have no idea what happened to their loved ones.

"100 days after MH370 went missing, its loss remains a painful void in the hearts of all Malaysians and those around the world," Transport Minister Hishammuddin Hussein said in a statement.

"We cannot and will not rest until MH370 is found."

On Saturday, Prime Minister Najib Razak posted on his Twitter feed the 100th day should be marked by "remembering those onboard and their families. Malaysia remains committed to the search effort".

Malaysia's scandal-prone government has come under fire from anguished relatives over the lack of information which -- along with the unprecedented nature of the incident -- has fuelled accusations by some families of a cover-up.

Stephen Wang, whose 57-year-old mother was aboard, greeted the renewed Malaysian vow with scepticism.

"Malaysia has from the beginning said they will work hard to find the plane, and now we are no further than at the start. If they keep using this method of working hard, then there's not much hope," he told AFP.

- 'We want to know what happened' -

The Boeing 777 vanished en route from Kuala Lumpur to Beijing. No trace of it has been found despite an extensive Australian-led search effort deep in the Indian Ocean, where Malaysia believes it went down.

Theories on what happened include a hijacking, rogue pilot action or mechanical failure.

But with no wreckage or other clues available, it remains one of aviation's greatest mysteries and hopes are slim of finding any firm evidence in the ocean.

"We want the plane to be found. We want to know what happened," said Subramanian Gurusamy, a Malaysian whose 34-year-old son was aboard, when asked of his government's latest pledge.

Hishammuddin said Malaysia "cannot and will not abandon" MH370 families, and thanked Australia, China, the United States and fellow Southeast Asian countries for their assistance in the still-futile search.

Malaysia's 57-year-old ruling regime denies withholding information.

But it has remained tight-lipped over investigations it launched into the mystery, and has given no timetable for when any findings will be released.

Sceptical MH370 families launched a drive earlier this month to raise $5 million to reward any insider willing to come forward with information.

On Sunday, around 20 relatives in t-shirts emblazoned with "pray for MH370" prayed and burned incense in a memorial to mark the 100th day since the plane's disappearance at a Buddhist temple in Beijing, with some openly weeping.

Two-thirds of the flight's 227 passengers were Chinese.

A Facebook page for MH370 relatives filled Sunday -- Father's Day -- with poignant messages marking the 100th day and remembering the fathers aboard.

"Dear father, a year has passed and its Father's Day again -- can you still hear me?" asked a letter in Mandarin, signed by Dou Jialei.

Another letter signed by Cheng Liping said: "Every minute of the day I am calling for my husband in my heart, and my children are calling for their dad to come home quickly."

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