Prime Minister Tony Abbott says searchers are "hopeful but by no means certain" that a pulse signal detected by a Chinese ship in the Indian Ocean is related to missing Malaysia Airlines flight MH370.

Mr Abbott has urged caution following the most recent finding in a trail of disappointing leads to date.

"We need to be very careful about coming to hard and fast conclusions too soon," he said.

"This is the most difficult search in human history. We are searching for an aircraft which is at the bottom of a very deep ocean and it is a very, very wide search area."

Retired Air Chief Marshal Angus Houston, who is leading the international search effort, said the pulse signals are characteristic of an aircraft black box.

"I have been advised that a series of sounds have been detected by a Chinese ship in the search area," he said in a statement this morning.

"The characteristics reported are consistent with the aircraft black box.

"A number of white objects were also sighted on the surface about 90 kilometres from the detection area.

"However, there is no confirmation at this stage that the signals and the objects are related to the missing aircraft."

The vessel Haixun 01 picked up the signal for about 90 seconds using a black box detector, China's Xinhua news agency reported.

The agency said the signal had a frequency of 37.5 kilohertz - the same as those emitted by flight recorders.

It said the signal was detected at about 25 degrees south latitude and 101 degrees east longitude, in the search zone about 2,000km off the West Australian coast.

Air Chief Marshal Houston says the Australian Maritime Safety Authority's Rescue Coordination Centre (RCC) has spoken to the RCC in China and asked for any further information that may be relevant.

"The deployment of RAAF assets to the area where the Chinese ship detected the sounds is being considered," he said.

The reported location of a pulse signal detected by a Chinese vessel in the search for signs of flight MH370. ( Google Maps )

The black box is equipped with a locator beacon that transmits "pings" when underwater, but which only has an expected battery life of about 30 days. The Boeing 777 went missing on March 8.

Anish Patel, from the company Dukane Seacom, which produces the detection system for black box recorders, says the signals picked up by the Chinese ship are unlikely to be from anything other than a black box.

"There is very little in nature or in the background noise of the ocean that emits this frequency, so unless it is another vehicle or other beacon in the vicinity, which I really doubt in this part of the ocean, this is a positive sign," he said.

Foreign Minister Julie Bishop shares Mr Abbott's concerns, saying she does not want to raise false hopes.

"We are seeking more information from the Chinese vessel and from the Chinese authorities about it, so until such time as Angus Houston confirms it, I would say we should be very cautious about this information," she told the ABC's Insiders program.

Clear weather expected for today's search

Up to 10 military planes, 2 civil aircraft and 13 ships will scour today's search area, 2,000 kilometres north-west of Perth, in an effort to find wreckage from the plane.

The Australian Maritime Safety Authority has identified three separate search zones covering approximately 216,000 square kilometres. Weather in the area is expected to be clear.

"If we haven't found anything in six weeks we will continue because there are a lot of things in the aircraft that will float," Air Chief Marshal Houston said.

"Eventually I think something will be found that will help us narrow the search area."

The plane went missing with 239 people on board, including six Australians, after it vanished off radar screens during a flight from Kuala Lumpur to Beijing four weeks ago.

Dozens of flights by a multinational taskforce have so far failed to turn up any trace of the plane.

The plane was briefly picked up on military radar on the left side of Malaysia and analysis of subsequent hourly electronic handshakes exchanged with a satellite led investigators to conclude the plane crashed far off the West Australian coast.

Formal investigation into MH370's disappearance launched

Malaysia said yesterday it had launched an investigation into the disappearance of the flight that would comprise experts from around the world.

Authorities have not ruled out mechanical problems as a cause but say the evidence, including the loss of communications, suggests flight MH370 was deliberately diverted thousands of kilometres from its scheduled route.

Malaysia's defence and acting transport minister Hishammuddin Hussein told a news conference that Australia, China, the United States, the United Kingdom and France had agreed to send representatives to take part in the investigation.

The extensive search and rescue operation has so far included assets from 26 countries.

Under International Civil Aviation Organisation regulations, the country where the aircraft is registered leads the investigation when the incident takes place in international waters.

ABC/wires