Chinese team has scoured more than 200,000 sq km of Indian Ocean

The challenges faced by Chinese personnel involved in the search for Malaysia Airlines flight MH370 are "unprecedented", said national maritime search and rescue center deputy director Zhuo Li on Thursday.

Chinese operations in the multinational effort have covered more than 200,000 square kilometers in the area 1,850 km west of Perth, Australia. The area covered in the remote southern Indian Ocean is about one-third the size of China, Zhuo said.

Up to eight aircraft and nine ships were involved on Thursday in the hunt for MH370, which disappeared on March 8 en route from Kuala Lumpur to Beijing. The plane was carrying 239 people, including 154 Chinese passengers.

The search area, which Australia is coordinating, will be adjusted further north, said retired Australian air chief marshal Angus Houston.

In a briefing to Malaysian Prime Minister Najib Razak, who arrived at the base of the operations in Perth on Wednesday to meet those conducting the search, Houston said that Australia is doing everything it can to assist Malaysia to find MH370.

"It is the most challenging and demanding search and recovery operations I've seen and probably one of the most complex operations of this nature the world has seen," said Houston, who heads the Joint Agency Coordination Center coordinating the operation.

Najib also met his Australian counterpart Tony Abbott at the base and spoke to the commanders of the seven nations who were there as part of search efforts.

The eight planes and nine ships scoured about 223,000 square km, 1,680 km northwest of Perth on Thursday.

The Malaysian and Australian leaders pledged their commitment to find MH370.

Najib promised the families of the victims that Malaysia would not give up the search.

"I know that until we find the plane, many families cannot start to grieve. I cannot imagine what they must be going through. But I can promise them that we will not give up," he said.

Speaking at a joint news conference, Abbott also promised that Australia will not rest until it has done everything it humanly can in the search for the plane.

He said they cannot be "certain of ultimate success" in finding the plane but all countries were doing their best under very difficult conditions.

Abbott also asked the families to be patient and said Australia welcomes them when the time comes for them to go to Perth. Malaysia Airlines had promised to fly the families to Perth pending approval from authorities.

Australia's Prime Minister Tony Abbott (left) and Malaysia's Prime Minister Najib Razak tour Pearce Australian air force base near Perth on Thursday. A nuclear-powered submarine has joined the near-four week hunt that has so far failed to find any sign of the missing Malaysia Airlines flight MH370 and the 239 people onboard. Rob Griffith / Reuters