Malaysia Prime Minister Najib Razak will visit Australia to witness the race-against-time bid to locate a crash site for flight MH370, his government said Monday as a ship equipped to pinpoint its "black box" prepared to steam to the search area.

Ships and planes from seven nations scanned a vast zone far off western Australia for yet another day, but the hunt for debris that would prove the Malaysia Airlines jet crashed in the Indian Ocean more than three weeks ago turned up nothing.

"The prime minister, who is going to Perth on Wednesday, will be briefed fully on how things have been conducted, and probably will be discussing what are the chances ahead," Malaysian Transport and Defence Minister Hishammuddin Hussein told reporters in Kuala Lumpur.

Experts warn debris must be found within days to nail down a crash site in order for any use of the US-supplied black box detector -- known as a towed pinger locator (TPL) -- to be feasible.

The US Navy, which has supplied the detection device, said in a statement Monday: "Without confirmation of debris it will be virtually impossible to effectively employ the TPL since the range on the black-box pinger is only about a mile."

But Australian Prime Minister Tony Abbott said earlier in the day no time limit would be imposed on the search for clues as to what happened.

- 'We owe it to the world' -

"We owe it to the families, we owe it to everyone that travels by air, we owe it to the anxious governments of the countries who had people on that aircraft. We owe it to the wider world which has been transfixed by this mystery for three weeks now," Abbott said in Perth.

The Boeing 777 carrying 239 people vanished without a trace on March 8 en route from Kuala Lumpur to Beijing, leaving stunned relatives, the aviation industry, and ordinary travellers around the world hanging on the mystery.

Families of Chinese passengers have angrily attacked Malaysia, alleging incompetence and deceit in what even Malaysian officials call the "unprecedented" loss of a jumbo jet.

More than a dozen Chinese relatives -- part of a group of nearly 30 who arrived on the weekend to press for answers -- kept up the pressure after a prayer session Monday at a Kuala Lumpur Buddhist temple.

"We will never forgive those who hurt our families and don't tell the truth and delay the rescue mission," a spokesman for the group, Jiang Hui, told reporters, reiterating suspicions toward Malaysia voiced by many relatives of the 153 Chinese aboard.

The Australian vessel Ocean Shield, fitted with the pinger locator and an underwater drone designed to home in on the black box's signal, was to conduct sea trials off Perth on Monday before heading to the search area.

A black box signal usually lasts only about 30 days. Fears are mounting that time will run out -- Ocean Shield will not reach the search zone, now the size of Norway, until Thursday, Hishammuddin said, roughly 26 days after the plane went missing.

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

Malaysia believes MH370 was deliberately diverted by someone on board and that satellite data indicates it crashed in the remote Indian Ocean.

Monday's search saw ten planes take to the skies, with ten ships already at sea. Australia, China, Japan, New Zealand, Malaysia, South Korea and the US are taking part.

Malaysia remains officially in charge, but Australia has assumed increasing responsibility, appointing retired air chief marshal Angus Houston to head a new coordination centre in Perth.

Many Chinese relatives, still holding out slim hopes, have taken issue with Najib's March 24 announcement that the plane was lost at sea, despite the lack of firm evidence.

- Malaysian response 'clumsy' -

Hishammuddin said "high-level" Malaysian officials and experts involved in an investigation into MH370 would brief families simultaneously in Kuala Lumpur and Beijing "soon" in a bid to explain Malaysia's stance.

Malaysia insists it is being transparent, but is yet to release any details of its investigation into what happened, which has included probing the backgrounds of everyone on the flight, including its crew.

In testy exchanges with foreign journalists Monday, Hishammuddin said: "We are not hiding anything, we are just following the procedure that has been set."

Malaysia also has come under fire from China's state media, while Beijing has pressed for more transparency in the investigation. Authorities there allowed angry relatives to stage a rare protest last week at Malaysia's embassy.

But a commentary in the government-controlled China Daily struck a more measured tone Monday, urging relatives to accept their losses.

"Although the Malaysian government's handling of the crisis has been quite clumsy, we need to understand this is perhaps the most bizarre incident in Asian civil aviation history," it said.

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