Relatives of passengers on the missing Malaysia Airlines jet MH370 gathered at a temple in Beijing to mark the six-month anniversary of its disappearance, as a small band of plainclothes police pressured them to disperse.

While the family members ostensibly gathered on Monday morning to pray for their relatives, the meeting quickly turned into a demonstration.

The family members, most of them elderly, stood in a cluster at the gates of the Lama Temple in central Beijing, wearing T-shirts that read "pray for MH370 to peacefully return home". Many of them sobbed and one man recited poems he had written since the plane vanished. Only a few minutes into the demonstration, plainclothes security officers broke through a ring of camera-wielding journalists and shouted for him to stop.

Eventually, they succeeded in subduing the crowd, shoving the journalists away and dragging women by the wrists. "Where are our children?" cried one woman. "Mum and dad are waiting for you!" cried another.

"I think Malaysia Airlines and the Malaysian government are cheating people – and while the whole world is watching, nobody will tell us anything," Dai Shuqin, 61, whose sister was on the plane, said before the demonstration. "We don't know if [Chinese president] Xi Jinping knows anything or not, but if he does know something, we hope he'll tell us."

Victims of perceived injustice in China have few formal channels to air their grievances – the country's media and courts are controlled by the government, there are few civil society groups and so many family members of Chinese passengers have turned to protests, online posts and uncensored foreign media to make themselves heard.

Some family members say that authorities have begun to treat them like dissidents. In July, police detained about 30 family members, including two young children, for attempting to sleep at a MH370 relatives support centre, Dai said, despite permission from centre staff to do so. At least two family members were beaten in detention, she said.

"It makes me so sad that they'd treat us this way, because we haven't done anything illegal," said Bian Liangwei, a 26-year-old resident of neighbouring Hebei province, whose older brother was on the flight. Bian said that he and other relatives have written to the Malaysian and Chinese governments, to the airline, even to the United Nations, in their quest for information. Local lawyers have refused to help them because of "issues with international law", and domestic journalists have been barred from writing extensively about their plight.

Bian said the airline had offered the families of passengers USD $50,000 (about £30,000) each in compensation. Most families have refused the offer. "All we care about is getting back our relatives," Bian said. "Without any proof that they're dead, we can only assume they're still alive."

No trace of MH370 has been found since the Boeing 777 became unresponsive and veered off course while travelling from Kuala Lumpur to Beijing on 8 March with 239 passengers and crew on board, 154 of them Chinese. International investigators have used satellite information to narrow the search area down to a 60,000 square kilometre area of the Indian Ocean west of Australia. Investigators suspect that the plane may have been deliberately diverted – yet even if they find the wreckage, they say, it has been underwater for so long that it may not reveal what caused the greatest aviation mystery in recent history.