BEIJING/KUALA LUMPUR (AFP) - Frustrated family members of the Chinese passengers aboard missing flight MH370 walked out of a briefing by Malaysian officials on Friday, leaving the panel to stare at ranks of empty chairs while a relatives' representative berated them.

With the search into its 20th day, hundreds of family members of the 153 Chinese passengers stood up about an hour into a briefing at Beijing's Lido Hotel and calmly filed out of the room, in a surreal scene that underscored the simmering tensions between the relatives and Malaysian authorities.

The man who led them in protest - a representative of the families who gave only his surname Jiang - took the microphone as soon as officials opened the floor for questions following their presentation on the latest details of the search effort.

Mr Jiang, who was wearing a white MH370 T-shirt underneath a tan blazer, turned to the relatives and asked them whether they were satisfied with what they have heard from officials so far.

"No!" the family members responded in unison.

He led them in leaving the hall, as cameras rolled and the panel of Malaysian officials wordlessly looked on. Several dozen uniformed police officers stood on the sides of the room, watching the scene unfold.

Once the family members had left, Mr Jiang returned and took a seat in the front row, directly in front of the officials.

"You have seen from the scene today that the next of kin are united," he declared. "Chinese people are united. The facts which you have been concealing - or trying to conceal - will ultimately see the light of day. There will certainly be people who receive their due punishment as a result of this."

Lieutenant-General Ackbal Abdul Samad, commander of the Malaysian Air Force operations, responded by defending the search operation and maintaining that the authorities were working their hardest.

"We are trying our best. We are trying our best," he said.

With a twinge of exasperation in his voice, he added: "We have got nothing to hide."

The back-and-forth soon ended, Mr Jiang left the hall and the panel of Malaysian officials sat quietly, staring out at the rows of empty seats in the ballroom.

The bizarre scene was in dramatic contrast to irate relatives scuffling with security personnel outside the Malaysian embassy in Beijing on Tuesday, after authorities allowed a rare protest march in the capital.

After several minutes, a reporter broke the silence to ask the officials what they were waiting for.

Mr Jiang then returned and announced that the family members were to hold a private meeting in the hall - no journalists or officials allowed.

The panel remained silent for another moment. Relatives began flooding back into the room.

"Seems we'll take a leave," said Lieutenant-General Ackbal Abdul. "And then we'll see what's next."

Meanwhile in Kuala Lumpur, relatives of the Chinese passengers have demanded China mount its own inquiry into the disappearance, a letter shows.

The document, sent to Beijing's special envoy in Kuala Lumpur, denounced Malaysia's handling of the search and asked the Chinese government to set up its own "investigation office".

News of the letter comes as a committee set up by relatives of the 153 Chinese passengers has begun discussions with lawyers about a potential lawsuit against Malaysia Airlines, a move that the family members have hotly debated among themselves.

"We question Malaysia's motivations in misleading and delaying so as to miss the best moment to find MH370," the relatives wrote in the letter to special envoy Zhang Yesui on Thursday, blasting Kuala Lumpur's behaviour as "irresponsible" and "inhumane".

"We earnestly request that China establish an investigation office into MH370," the letter states, also urging "an effective communication system between the relatives and the government".

Beijing has urged Kuala Lumpur to include Chinese experts in its own investigation, but has not so far spoken of setting up its own inquiry into the flight.

The family members' requests to the Malaysian government listed in the letter include an official apology, along with return airfares to Malaysia and the provision of food and accommodation until the resolution of the search.

The family members hailed Beijing's efforts but also called for greater support, including legal assistance and the full participation of Chinese authorities in the search.

"Uphold the rights and interests of the people. Do not simply give up," the letter reads. "Exhibit the demeanour of a great nation!"

According to China's official Xinhua news agency, Mr Zhang met family members of the passengers on Thursday in Kuala Lumpur.

"Our goal is to make every effort to find our missing countrymen," he told them, according to Xinhua.

As anger over Malaysia's handling of the search simmers, some relatives posting in a group on China's popular WeChat social messaging app debated the issue of whether to seek legal assistance.

A committee formed by the families has been in contact with the Ribbeck Law Firm in Chicago about a potential lawsuit against Malaysia Airlines, the state-run China Daily newspaper reported on Friday.

But several family members posting to the WeChat group on Friday urged that it was too early to discuss the idea of a lawsuit or compensation.

"We still don't know the truth; don't waver," wrote one relative. "Sooner or later, we will get compensation, with our country behind us, so what's the rush?"

Another wrote: "Anyone who is talking with lawyers about compensation right now doesn't even count as human."