Perth: An Australian ship carrying equipment to locate the "black box" from flight MH370 was to put to sea Monday but experts warned surface debris must be found first to narrow down the search zone.
The hunt for physical evidence that the Malaysia Airlines jet carrying 239 people crashed more than three weeks ago, as Kuala Lumpur has declared, has so far proved fruitless despite a massive operation involving seven countries.
Hopes raised by debris sightings have repeatedly been crushed as the items turned out to be random sea junk such as fishing gear.
More objects were seen by aircraft on Sunday with several items retrieved by Australia`s HMAS Success and China`s Haixun 01, but the Australian Maritime Safety Authority said: "Nothing has yet been verified as being from MH370."
The growing search resumed Monday across a sweeping expanse of the southern Indian Ocean the size of Norway, with 10 planes taking to the skies from Australia, China, Japan, New Zealand, Malaysia, South Korea and the US.
Ten ships are also now scouring the desolate seas 1,850 kilometres (1,150 miles) west of Perth for clues, with seven from China, two from Australia and a merchant vessel. AMSA warned that "some parts of the search area will experience low cloud and rain throughout the day".
Australia`s Ocean Shield, fitted with a US-supplied black box detector, known as a towed pinger locator, and an autonomous underwater vehicle that can comb the seabed using electronic sensors, was also to leave Perth.
But Captain Mark Matthews from the US Navy, who was involved in the search for an Air France jet which crashed into the Atlantic Ocean in 2009, said the crash site must be identified first to allow any pings from the recorder to be located.
"It is critical that we find that surface debris so we can reduce the area that we`d need to conduct an underwater search in," he told the Australian Broadcasting Corporation.
"Right now the search area is basically the size of the Indian Ocean, which would take an untenable amount of time to search."
With MH370 vanishing on March 8 and a black box usually giving off signals for 30 days there are fears that it could already be too late with Ocean Shield taking up to three days to get to the area, although Matthews said the pinger could last up to 15 days longer than that.
Australian Navy Commodore Peter Leavy, the commander of the military arm of the search, said the focus Monday was still to find debris and confirm it was from the plane then work backwards to a possible crash site.
"The search area remains vast and this equipment can only be effectively employed when there is a high probability that the final location of Flight MH370 is better known," he said.
While Malaysia remains in charge of the search operation under international protocols, Australia has assumed increasing responsibility with retired air chief marshal Angus Houston on Sunday appointed to head a new joint agency coordination centre in Perth.
His job will involve coordinating diplomatic contacts between search participants and ensuring families get all the information and help they need.
About two-thirds of those on board the plane were Chinese and many of their families have been highly critical of the way Malaysia has treated them, accusing Kuala Lumpur of providing insufficient information as they endure an agonising wait to learn the fate of their loved ones
Malaysia believes the flight was deliberately redirected by someone on board, but nothing else is known.
Relatives of Chinese passengers arrived Sunday in Kuala Lumpur -- some angrily seeking answers and others seeking closure.
Many passengers are particularly incensed at the announcement on March 24 by Prime Minister Najib Razak that -- based on detailed British analysis of satellite and other data -- the plane had been lost at sea.
Clinging to shreds of hope, several desperate relatives refuse to accept this until wreckage is found.
"Tell us the truth. Give us our relatives back," read one poster displayed Sunday by the Chinese relatives who travelled to Malaysia.
But not all were in militant mood.
At a regular briefing by Malaysian officials for family members in Beijing, a woman said not all the group members took the trip to put pressure on the Malaysian government.
"Some of the next of kin want to see for themselves the last place where their loved ones ever set foot," she added, breaking down in tears.