A Chinese ship has twice detected a pulse signal with characteristics of an aircraft black box, while an Australian vessel is also investigating a separate "acoustic noise" in the search for flight MH370.

The Chinese ship, Haixun 01, has picked up the pulse signal on two separate occasions within a two-kilometre zone since Friday.

Retired Air Chief Marshal Angus Houston, who is leading the international search effort, said the second detection occurred on Saturday afternoon.

"This morning (Sunday) we were contacted by the Chinese authorities and advised that Haixun 01 had late yesterday afternoon redetected the signals for 90 seconds within just two kilometres of the original detection," he said.

"This is an important and encouraging lead, but one which I urge you to continue to treat carefully.

"We are working in a very big ocean and within a very large search area and so far, since the aircraft went missing, we have had very few leads which allow us to narrow the search area."

Air Chief Marshal Houston said the Australian vessel Ocean Shield and British ship HMS Echo would be redeployed to assist the Haixun 01.

However, he said the Ocean Shield would be delayed while it investigated a separate "acoustic event".

"We are looking at several hours to a couple of days" for the Ocean Shield to look at the separate acoustic lead, Air Chief Marshal Houston said.

He urged caution about jumping to conclusions about the nature of the signal picked up by the Haixun 01.

"What we have got here are fleeting, fleeting acoustic events," he said.

"The one the night before last lasted just a very short period of time. The one yesterday (Saturday) afternoon, I think it was 15:47 in the afternoon, was for 90 seconds. That's all we have got.

"It's not a continuous transmission. If you get close to the device, we should be receiving it for a longer period of time than just a fleeting encounter.

"But we have got a transmission, we must investigate it. That's the way we work."

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

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

Air Chief Marshal Houston said aircraft would be deployed to the area where the Haixun 01 detected the signal.

Houston says China sharing everything of relevance

Flight MH370 went missing on March 8 with 239 people on board, including six Australians.

The majority of the passengers on board were Chinese, and Malaysian officials have repeatedly come under fire from their families for the way the search has been handled.

Reports of the signal being detected by the Haixun 01 first arose through the Chinese media, but Air Chief Marshal Houston said "China is sharing everything that is relevant to the search".

"Let me just say ... China has seven ships out there - that's by far the largest fleet of ships," he said.

"They are out there looking for this aircraft and at the moment the most promising lead appears to be the one associated with the Haixun 01.

"I think we should be focusing on the positives and not start saying 'Are they doing this or doing that?'

"I'm very satisfied with the consultation, the coordination we are building with our Chinese friends. I spent two hours last night with the Chinese ambassador and we worked out the best way to effect that coordination and consultation for my responsibilities. I'm very, very happy about that."

Air Chief Marshal Houston said the revelation of the acoustic event being investigated by the Ocean Shield was "late breaking news" at the time of his press conference, about 1:30pm (AEST).

He echoed Prime Minister Tony Abbott's sentiments about providing information to the public as soon as it is available.

"I thought it was important that we are totally transparent with you," he said.

"I just want you to know that the search is a dynamic thing. Things are happening all the time."

Time running out in hunt for black box

The black box only has power to fire the signal for about a month, meaning the pulse is set to die any day now.

China's Xinhua news agency has reported 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.

Anish Patel, from the company Dukane Seacom, which produces the detection system for black box recorders, said the signals picked up by the Chinese ship were 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.

However, Air Chief Marshal Houston said officials were "a long way from making any conclusion" on the nature of the signal.

"The water in which the Haixun 01 is working at the moment - it is very, very deep. I think it's in the order of 4-4,500 metres," he said.

"That's incredibly deep - 4.5 kilometres straight down - so any recovery operation is going to be incredibly challenging and very demanding and will take a long period of time. That's if there is anything down there.

"First of all we have got to establish the fact that there is something down there. We are a long way from making that conclusion.

"That's why we need HMS Echo and the Australian Defence vessel Ocean Shield to come to the location, because they have special equipment that can help us make the judgment whether there is anything down there.

"But I think the fact that we have had two detections, two acoustic events, in that location provides some promise which requires a full investigation of the location."