MH370: 'Black box' ship due in search zone

Australian navy vessel Ocean Shield, which is fitted with a US-supplied "black box" detector, was Friday expected in the area being scoured for wreckage of Flight MH370 as 14 planes continued the arduous search.

Nearly a month after the Malaysia Airlines jet carrying 239 people vanished authorities still have no idea how or why it crashed and warn that unless the black box is found, the mystery may never be solved.

But finding the flight data recorder using the towed pinger locator on Ocean Shield appears increasingly remote with officials warning that without a confirmed crash site, hopes of recovering the device are slim in the vast and unpredictable southern Indian Ocean.

Time is also ticking with the battery-powered signal from the black box expected to expire within days. Ocean Shield left Perth on Monday evening for the three-day voyage to the search zone.

The British navy's hydrographic ship HMS Echo is already in the area and spent Thursday scouring for sonic transmissions from the flight data recorder.

"One alert was experienced but discounted," the Perth-based Joint Agency Coordination Centre (JACC) said.

"False alerts may be experienced from biological sources such as whales or interference from shipping noise."

Weeks of looking for wreckage of the plane that veered off course en route from Kuala Lumpur to Beijing on March 8 have proved fruitless despite eight nations now involved in the increasingly desperate hunt for clues.

They drew another blank on Thursday with 10 military planes, four civil jets and nine ships due to resume the search on Friday, zig zagging across a huge area of about 217,000 square kilometres, 1,700 kilometres northwest of Perth.

"The weather forecast for today's search is fair, with visibility approximately 10 kilometres and a cloud base between 1,000 and 2,000 feet," JACC said.

If floating MH370 debris is eventually found, authorities plan to analyse recent weather patterns and ocean currents to determine where the plane went down.

Malaysia believes the flight was deliberately diverted by someone on board and that satellite data indicates it crashed in the Indian Ocean.

Malaysia's disjointed response to the crisis has been widely criticised, particularly by distraught relatives of the 153 Chinese people on the plane, and Australia has assumed increasing responsibility in the quest to find answers to one of aviation's greatest mysteries.

Prime Minister Tony Abbott on Thursday said there were no current plans to scale back the search but cautioned that a reassessment would have to be made eventually.

On a tour of the Perth military base being used as the staging post for the search effort on Thursday, Malaysian Prime Minister Najib Razak vowed "we will not rest" until the fate of flight was known.

"We want to find answers. We want to provide comfort to the families and we will not rest until answers are indeed found," he said, while admitting it was a "gargantuan task".