A search for two large objects that may be from the missing Malaysia Airlines jet has concluded for the day without any sight of flight MH370.
Friday's operation involved five aircraft, including three RAAF Orions, and a US Navy P8 Poseidon which scoured a remote area in the southern Indian Ocean of 8,800 sq miles (23,000 sq km).
Malaysia has now asked the US to provide underwater surveillance equipment to help in the search for the missing plane.
And a former air accident investigator told Sky News he believed the disappearance of MH370 was the result of a "criminal act".
Despite returning to Perth after failing to find any evidence of debris from the missing aircraft, Australian air crews remained hopeful.
Flight lieutenant Russell Adams said conditions had been perfect but there was no sign of any wreckage.
He said: "Unfortunately the conditions back here precluded us from staying on station as long as we'd like, however there are other aircraft out there still searching.
"We've got a lot of hope. Hopefully we'll find something soon."
But Australian deputy prime minister Warren Truss admitted the objects spotted on satellite images in the remote southern Indian Ocean may have sunk.
"Something that was floating on the sea that long ago may no longer be floating," he told reporters in Perth.
"It may have slipped to the bottom."
At a news conference in Kualar Lumpur the Malaysian authorities said they were using every possible search and rescue asset in the world to help them find the missing aircraft.
Britain's HMS Echo is on its way and David Cameron told his Malaysian counterpart that Britain stands ready to help with whatever specialist support they can offer.
Meanwhile, former assistant director of the FBI in New York James Kallstrom, who investigated the explosion of the Boeing 747 flight TWA 800 12 miles out into the Atlantic Ocean in 1996, told Sky News he thought a "criminal act" was to blame for the plane's disappearance, and felt the the main focus of the inquiry should be the crew.
And on the search operation, Mr Kallstrom said the Malaysian authorities had not been co-ordinated, and were "slow on the uptake".
He said: "I don’t blame them for that because these things are overwhelming, when this happens it is overwhelming.
"But they were slow to come up with this thing, and they were slow to take help.
"In retrospect they should have asked us to come over there right away. Not because we are superior in any way but because we’ve got so much more experience."
It was also revealed the plane could have been carrying lithium-ion batteries in the cargo hold.
The flammable batteries can pose a safety concern and are required to undergo stricter testing than other types of battery.
In Boeing's 787 Dreamliner's first year of service, some four aircraft experienced problems stemming from its lithium-ion batteries.
But Malaysia Airline's chief executive, Ahmad Jauhari Yahya, told Sky's Kay Burley the batteries were an approved item and were not classed as dangerous goods.
"We carry some lithium ion batteries but they are approved and not declared as dangerous goods," he said.
"Airlines do this all the time; these goods have been flown many times."
Meanwhile, Australia's Prime Minister Tony Abbott said the country was doing everything it could to find the suspected debris and to keep the families of the passengers informed of the progress.
"We owe it to the families, the friends and the loved ones of the nearly 240 people on board flight MH370 to do everything we can to resolve what is as yet an extraordinary riddle," he told a news conference.
"Because of the understandable state of anxiety they’re in, we also owe it to them to give them information as soon as we get it to hand.
"We have five aircraft searching the area. We’re looking for a visual that was picked up on satellite imagery and as soon as we have additional information we’ll make it available."
A Norwegian merchant ship - the first vessel to reach the vicinity - has been using searchlights through the night to try to locate the objects.
They were spotted by a satellite last Sunday and could potentially be debris from flight MH370, one of which is thought to be 24 metres in length and the other about five metres.
The sightings have been deemed "credible" and a "potentially important development" by authorities - as the search for the passenger plane enters its 14th day.
Australian naval vessel HMAS Success, which is capable of retrieving debris, is also en route to the search area but is some days away.
There has been no trace of the aircraft since it vanished from radar a short distance into a flight from Kuala Lumpur to Beijing on March 8.
Wider searches, including of a northern corridor from northern Thailand to Kazakhstan, are set to continue until investigators are certain they have located the plane. Some 18 ships and 29 aircraft are taking part.
Those areas were targeted after faint electronic "pings" picked up by one commercial satellite suggested flight MH370 flew on for at least six hours after it disappeared from air traffic control screens.
Willie Walsh, chief executive of the International Airlines Group, said he was baffled by the disappearance of the aircraft.
"My deepest sympathies to everybody associated with this, it must be truly awful for the families and friends of the passengers and crew," he told Sky's Jeff Randall Live.
"I'm baffled; I must have heard twenty, thirty, maybe even forty theories on what has happened and quite honestly, we just don't know.
"I've been in this industry 35 years and I've never seen anything like this. I'm confident that with the technology today and the fact accident investigation has progressed significantly, we will ultimately find out."