Today marks the six month anniversary of the disappearance of MH370, which vanished without trace en route from Kuala Lumpur to Beijing with 239 people on board.

Investigators say what little evidence they have to work with suggests the plane was deliberately diverted thousands of kilometres from its scheduled route before eventually plunging into the Indian Ocean.

But no one knows for sure, or why. A painstaking international search has failed to find any trace.

About two thirds of those on board the flight were from China.

Relatives have been marking the six-month anniversary since the plane disappeared.

In Beijing, about 30 relatives gathered at one of the Chinese capital's most famous Buddhist temples.

For the relatives, their quest for answers has eased, and that seems to have become an annoyance for China's authorities.

Police have beaten at least two people whose children were on the flight, several family members said.

In one case, a woman in her 50s was hospitalised for three days.

"I went to see her in hospital, I could see the injuries on her head and body," said Zhang Yongli, 64, whose daughter was on the flight.

"The way the police acted was very extreme, it's wrong to treat us this way."

Beijing police did not respond to requests for comment.

China's government has repeatedly said it would spare no effort in the search for the plane and leaders have expressed sympathy for the families.

Public security authorities have not commented on the families but Malaysia Airlines representatives said distraught relatives have sometimes been aggressive.