A major search has been taking place in the southern Indian Ocean for two large objects that may be from the missing Malaysia Airlines jet.
Four long-range surveillance planes scoured a remote area of 8,800 sq miles (23,000 sq km) in an operation hampered by bad weather.
It lasted until last light and is set to resume Friday morning.
The objects were spotted by a satellite last Sunday and could potentially be debris from flight MH370.
The Australian Maritime Safety Authority (AMSA) said they were a "reasonable size", with one around 24 metres in length and the other about five metres.
But rain and cloud limited the visibility for the search crews, which were unable to locate the objects.
The country's prime minister, Tony Abbott, described the satellite sighting, around 1,550 miles (2,500km) southwest of Perth, or four hours by plane - as "credible" and a "potentially important development".
Malaysia's transport minister, Hishammuddin Hussein, called it a "credible lead".
The objects were spotted in the far south of the southern air corridor that investigators have been scouring over the last few days, along with an arc further north.
Satellite images, which show the two objects floating on or just under the surface, were taken on March 16 but it has taken time to analyse the pictures, and the objects would have moved since then.
However, more satellites are being redirected in the hope of getting higher resolution pictures.
Two Royal Australian Air Force Orion aircraft, a New Zealand Orion and a US Navy Poseidon aircraft have been involved in the search.
"The task of locating these objects will be extremely difficult and it may turn out they are not related to the search for MH370," Mr Abbott warned.
A Norwegian merchant ship has arrived in the vicinity, and the Australian naval vessel HMAS Success, which is capable of retrieving debris, is some days away.
A British naval survey ship, HMS Echo, is also heading to the region.
The wider searches, including a northern corridor from northern Thailand to Kazakhstan, will go on 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.
John Young, from the AMSA, cautioned the objects could be seaborne debris along a shipping route where containers can fall off cargo vessels, but the larger object is longer than a container.
British satellite telecommunications firm Inmarsat said there were "indications that 10 days ago MH370 would be found either in the southern part of the Indian Ocean or in central Asia - and not in the South China Sea or the Malacca Straits".
It said it had "never been critical" of the probe or told authorities to "look in this area", and that the information was only a small part of the expertise Malaysian officials were receiving.
The firm confirmed the Malaysian authorities were given this information, through an intermediary company, on March 12.
The depth of the ocean in the latest search area is around 3,500-4,000 metres.
This is a similar level to where the Air France plane wreckage was found after the jet crashed in the Atlantic in 2009.
The search for the missing Boeing 777, which had 239 people on board, has been focused on the two corridors, one of which extends towards the southern reaches of the Indian Ocean.
Military planes from Australia, the US and New Zealand have been scouring the vast search area, which was halved in size to 118,000 sq miles (305,000 sq km) on Wednesday.
There has been no trace of the aircraft since it vanished from radar a short distance into a flight from Kuala Lumpur to Beijing 12 days ago.
Willie Walsh, chief executive of IAG, which owns British Airways and Iberia told Sky's Jeff Randall that during his 35 years in the aviation industry, he had never seen anything like the disappearance of jet MH370.
Mr Walsh also told Sky News the Boeing 777 is "one of the safest aircraft in the world."
In Beijing, relatives of many of the 154 Chinese passengers waited anxiously for more news.
Sky's Jonathan Samuels, who is with the families, said: "They look exhausted. Most have slowly returned to their rooms to await developments from Australia."
Investigators believe two vital pieces of communication equipment were intentionally switched off and the aircraft deliberately diverted, potentially taking it thousands of miles off course.
Satellite data suggests the plane flew for at least seven hours after it was diverted west across Malaysia towards the Strait of Malacca.
Investigators are considering a number of theories about what happened to the aircraft, including hijacking, sabotage and terrorism.
However, background checks on all foreign passengers apart from three from Ukraine and Russia have yielded "no information of significance", Mr Hishammuddin said.
One theory that has gathered pace among aviation experts in recent days is that a fire in the cabin of flight MH370 may explain the mystery.
Pilot Fikri Zambi said the crew may have disabled tracking devices in response to a blaze and turned back towards the nearest airport, before being incapacitated by smoke.
The aircraft would then continue flying in auto-pilot mode, until it succumbed to the flames or ran out of fuel.