CANBERRA/BEIJING, April 28 -- Search for missing flight MH370 enters a new phase to a much larger seabed area after U.S. submarine drone Bluefin-21 found no clues of interest in the focus area, while China says it will continue to provide adequate resources for the search.

Australian Prime Minister Tony Abbott said Monday that the hunt for missing flight MH370 entered a new phase with seabed search to be expanded to a much larger area.

"We are moving from the current phase to a phase which is focused on searching the ocean floor over a much larger area," Abbott told a press conference after U.S. submarine drone Bluefin-21 completed a sea floor search of a focused area in the Indian Ocean and found no contacts of interest.

The focused area was defined as a circle of 10 km radius around the spot where the second suspicious signal of aircraft black boxes was heard on April 8.

Abbott said it is highly unlikely to find any aircraft wreckage on the ocean surface at this stage, indicating the visual search currently conducted by airplanes and vessels may be called off.

Fifty-two days have passed since the Malaysian Airlines flight disappeared en route from Kuala Lumpur to Beijing on March 8, but nothing related to the plane has been found.

Abbott said the new phase of search would involve commercial contractors specialized in deep ocean search and may take six to eight months if weather conditions permit.

Contractual equipment could be deployed in weeks and the Bluefin-21 would continue its mission in adjacent areas, he added.

"The Bluefin-21 submersible will continue in operation. What we are doing though is looking to an intensified underwater search involving different technology, in particular using specialized side scan sonar equipment towed behind ships to scan the seabed for evidence of aircraft wreckage."

In addition, an Australian aircraft, most likely a P-3C Orion, will be on standby at short notice in case possible wreckage is identified.

The new phase involving commercial contractors is expected to cost 55.8 million U.S. dollars.

Acknowledging that it is possible to never find the ill-fated plane, Abbott vowed to continue the search as thoroughly as "humanely possible."

Despite the fruitless search over the past weeks, Abbott said he still has "considerable degree of confidence" that the signals detected by U.S.-supplied towed pinger locator came from aircraft black boxes.

He also confirmed that Australia would maintain the leadership of the search operation while the Malaysians have indicated that they want Australia to be involved in all subsequent investigations.

Ma Zhaoxu, Chinese ambassador to Australia, said in Canberra on Monday that China will continue to provide adequate resources for the search of flight MH370.

Beijing also hoped that other countries will continue to contribute to the hunt, he said at a joint press conference with Angus Houston, chief of the Australian Joint Agency Coordination Center (JACC).

When asked to respond to Abbott's remarks on Monday, Chinese Foreign Ministry spokesman Qin Gang said in Beijing that China will continue communication and cooperation with Malaysia and Australia, positively support and participate in the new phase of searching for MH370.

Qin said China welcomes Australia's coordination of the deep ocean search, and called on the international community to continue the hunt.

"It is an unprecedented operation," Qin said.

The China Maritime Search and Rescue Center said in Beijing on Monday that it will adjust search operations for flight MH370 and intensify the underwater search.

The Chinese center said it will dispatch new vessels that can meet the needs for undersea search to join the operation and continue to cooperate with other countries.

Japanese Defense Minister Itsunori Onodera said in Perth that following a directive issued by the Australian government, Japan's Self-Defense Force (SDF) personnel who were deployed to help search for missing MH370 were told on Monday that their aerial searches have been disbanded.

The P-3C surveillance plane and the SDF personnel were given orders to return to Japan from the Australian Air Force's base near Perth around Thursday this week, Onodera said.