Separately, an Australian search vessel, the Ocean Shield, detected an "acoustic event" about 300 nautical miles north of the Chinese signal reception area.

The main search, though, centres on the region where a Chinese patrol ship Haixun 01 received a pulse signal with a frequency of 37.5 kHz - similar to flight recorders - on Friday and again on Saturday, within two kilometres of each other.

"The fact we've had two acoustic events in that location provides some promise, which requires a full investigation of the location," Air Chief Marshal (ret) Angus Houston, the head of the search's Joint Agency Coordination Centre, told a media conference in Perth on Sunday.

The UK's HMS Echo, a vessel equipped with underwater search technology, will be diverted to join the Chinese search area and will reach it in about 14 hours.

Friday's signal, which lasted for 15 minutes, was consistent with the standard frequency used by emergency locator devices on planes. China, though, said other ships in the area may have "disturbed" the signal at the time.

On Saturday, the Haixun recorded the frequency for about 90 seconds. The patrol boat is operating in waters more than four kilometres deep.

Unverified

Air Chief Marshal (ret) Houston stressed there has not been verification that any of the acoustic events reported are linked to the missing flight's black box, and that in the search's 30 days there have been numerous leads that have failed to locate the missing plane.

"This is a painstaking process and if we get any lead whatsoever we investigate it," he said.

"It is something that takes time.  We're dealing with very deep water, we're dealing with an environment where sometimes you can get false indications, there are lots of noises in the ocean and sometimes the acoustic equipment can rebound, echo."

Verification could be days or, even weeks away and even if there is confirmation, it could take a significant time before recovery of the devices, he said.

'Acoustic event'

The Ocean Shield, in its search, is towing a US black box "pinger locator" and reported the discovery just an hour before Sunday's media briefing in Perth.

"It's something that needs to be investigated," he said, adding the vessel carried sophisticated equipment. "The search is a dynamic thing."

The US equipment was still the search's best chance of pinpointing the flight recorders, he said.

The ship will remain in its current location and continue to investigate the signal detected Sunday morning, before possibly heading south towards the Haixun 01. A decision to relocate the ship would not be made until late Sunday.

Black box

The Malaysia Airlines flight MH370 with 239 people on board vanished without a trace after mysteriously changing course during a routine flight from Kuala Lumpur to Beijing on March 8.

The devices, known as the black box, activate when they come into contact with water and are attached to aircraft flight data and cockpit voice recorders. They often prove crucial in determining the causes of plane crashes but have a limited battery life, adding urgency to the search efforts.

"This is day 30 of the search and the advertised time for the life of the batteries is 30 days. Sometimes they last for 8 - 10 days after that, but we're running out of time," Air Chief Marshal (ret) Houston said.

The pulse signal was reportedly detected at 25 degrees south latitude and 101 degrees east longitude, in an area that appears to be outside the search parameters the Australian Maritime Safety Authority had said assets would be scouring on Saturday.

The Haixun crew had informed the China rescue coordination centre as well as Australian authorities, according to the Chinese state media report.

'Satisfied'

The Australian rescue coordination centre had not listed the Haixun 01 as part of the underwater search and it had not been widely known that the vessel was carrying equipment capable of detecting a block box signal.

China has "by far the largest" fleet in the search for plane, with seven vessels involved, Air Marshal Houston (ret.) said, adding he was "very satisfied" with the level of consultation with Chinese counterparts.

However, he said Australian Authorities were considering the addition of a Chinese liaison officer within the Australian rescue base.

The technical capabilities of the black box detection equipment on board the Haixun 01 remain unclear, but Air Chief Marshal (ret) Houston said the data the Chinese search vessel had provided was not enough to provide “means of verification” of whether it was related to the missing Malaysia Airlines flight.

This meant other naval assets carrying specialist underwater detection equipment, including the Royal Navy’s HMS Echo, would be redeployed to the area to “assist with either discounting or confirming” the findings.

“We have to do further investigation of the site itself,” he said.

Analysts have suggested that the early days of the international search effort had been hampered by a reluctance to share intelligence, particularly satellite imagery, that may reveal not just military technological capabilities, but also limits of that technology.

'Everything' shared

Air Chief Marshal (ret) Houston, though said he was “completely comfortable” with the level of information being provided by the Chinese government.

He said he was informed by the Chinese government of the Haixun’s findings “almost the same time” as Xinhua’s report first emerged on Saturday.

“China’s sharing everything that is relevant to this search – everything,” he said.

“I think we should be focusing on the positives and not start saying are they doing this or are they doing that.”

On Saturday night he revealed that white objects had also been sighted about 90 kilometres from the detection area, and Australian authorities were considering sending Royal Australian Air Force assets to the area.

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

Long hunt

An international search has been under way for the past four weeks after the jetliner disappeared on a flight from the Malaysian capital Kuala Lumpur en route to the Chinese capital Beijing.

Malaysian authorities declared 12 days ago that the plane was believed to have crashed in the southern Indian Ocean after satellite data revealed its course.

The hunt for the plane is being coordinated from Perth. As many as 12 planes - 10 of them military ones - and 13 ships will take part in Sunday's search for the missing plane.

Sunday’s search will focus on three separate search areas about 2,000 kilometres north west of Perth, totalling about 216,000 square kilometres.

Conditions are expected to be favourable, with the cloud base in the search area at about 750 metres above sea level, allowing visibility of more than 10 kilometres.