Dozens of angry relatives of Chinese passengers aboard the missing flight MH370 have demanded that Malaysia apologise for its handling of the investigation as they arrived in Kuala Lumpur from Beijing on Sunday.

About 50 more family members joined those who had earlier flown to Malaysia, saying they hoped to get more information from officials in the capital. Around two-thirds of the 239 people on board the flight were Chinese.

As the hunt enters its fourth week, search crews are no closer to finding the plane, which disappeared on 8 March after diverting from its scheduled flight path as it headed from Kuala Lumpur to Beijing. Ten ships and as many aircraft were scanning a vast area of the southern Indian Ocean on Sunday, far off the western coast of Australia.

"We want evidence. We want the truth. We want our relatives," the group chanted in Chinese as they staged a protest at a hotel near the Malaysian capital, holding banners reading: "We want evidence, truth, dignity" in Chinese, and "Hand us the murderer. Tell us the truth. Give us our relatives back" in English.

Representing the relatives, Jiang Hui said they wanted Malaysia to apologise for what they see as mistakes in its initial handling of the disaster and Monday's declaration that it had crashed into the southern Indian Ocean with the loss of all lives. They argue that conclusion – based on radar and satellite analysis – was premature given the lack of physical evidence.

Jiang said they wanted to meet senior officials from the airline and government as well as technical teams, complaining that they had not received satisfactory answers during meetings with Malaysian representatives in Beijing.

Ong Ka Ting, the Malaysian prime minister's special envoy to China, said that the government understood their feelings.

"We know that definitely by coming over here there will be a lot more discussions and meetings … So we try our best to assist them," he said.

Malaysia Airlines has said it will fly families to Australia if the wreckage of the plane is found.

Both Chinese and Australian vessels have found debris since authorities moved the search about 700 miles closer to Perth on Friday, but officials said the objects turned out to be unconnected to the missing Boeing-777.

Commodore Peter Leavy of the Australian navy said the teams needed to find items, establish they were from flight MH370 and then try to establish where the plane might have hit the water. Experts say that currents could have carried floating wreckage hundreds of miles from the main crash site by now.

Only then can specialist equipment be used to photograph possible debris on the seabed and help track the aircraft's black box flight data and cockpit voice recorders.

"The search area remains vast and this equipment can only be effectively employed when there is a high probability that the final location of flight MH370 is better known," Leavy said.

The electronic beacons on the black box is certified to emit signals for just 30 days – a deadline that is fast approaching.

But Captain Mark Matthews, the US navy supervisor of salvage and diving, said: "In my experience, they do last a little bit longer than that … I would say 45 days is the realistic limited expectation."

Australia has appointed its former defence force chief, Air Chief Marshal Angus Houston, to head a new joint agency co-ordination centre as more planes and ships join the search. The Perth-based centre will co-ordinate operations between the numerous countries involved in the hunt and keep families involved.

It has also issued rules and guidelines to all those involved in the search, stipulating that Australia will hold any wreckage found securely for Malaysian authorities, which will have authority in investigating it.