Rescue authorities are studying satellite data for more clues in the hunt for missing Malaysia Airlines Flight MH370, after an air and sea search in the remote Indian Ocean off Australia failed to find any trace of a suspected debris field.
Australia rushed four international aircraft to an area about 2500km southwest of Perth on Thursday when analysis of satellite images identified two large objects that may have come from the Boeing 777, which went missing from radar screens 13 days ago with 239 people aboard, including two New Zealanders.
China is also sending three warships to join the search in the southern Indian Ocean, the government said on Friday.
No indication has been give as to when they might arrive at the remote site, but earlier Chinese news reports said the ships - the Kunlunshan, the Haikou and the Qiandaohu - were searching near the Indonesian island of Sumatra.
A fourth Chinese vessel, the icebreaker Snow Dragon, is in the western Australian port of Perth following a trip to Antarctica and might join the search.
Investigators suspect the Malaysia Airlines flight, which took off from Kuala Lumpur for Beijing shortly after midnight on March 8, was deliberately diverted thousands of kilometres and then crashed into some of the deepest, most isolated waters on the planet in a possible suicide.
Rescue authorities cautioned that the objects spotted on the satellite images, dated March 16, might not be related to the transcontinental search for the plane but said the find represented the best lead yet.
The first search plane took off from Pearce RAAF base in Western Australia at 6.15am Perth time (11.15am NZT) today.
Yesterday's search was hampered by "extremely bad" weather conditions causing poor visibility, Australian air force pilots said.
Air Commodore Mike Yardley said the search area was known as the "roaring forties" owing to its treacherous conditions.
The satellite images showing possible debris of MH370 has given searches "a level of optimism", he said on TV3's Firstline this morning.
"But of course it's a huge ocean, a huge search area, and we've still got a task ahead of us," he said.
But Yardley was optimistic that the searchers will find the objects. "We will find it - I'm sure about that piece of it. The only reason we wouldn't find it was that it has sunk," he said of the large unidentified object spotted by the satellite.
"I've been on these missions before when it's taken a few days to come across it," he said.
Australian Prime Minister Tony Abbott this morning said Australia was "throwing all the resources we can at it [the search operation]".
A Norwegian merchant ship that had been diverted to the area last night was still searching there. Another vessel would arrive later today.
Acting Prime Minister Warren Truss said Australia continued to examine satellite footage to pinpoint the location of the suspected debris, which included a piece estimated from the satellite imagery to be 24 metres long.
"Clearly, there's a lot of resources being put into that particular area. It's broadly consistent with the flight plans that were talked about ever since the satellites and their work has been added to the information bank," Truss told ABC radio.
"That work will continue, trying to get more pictures, stronger resolution so that we can be more confident about where the items are, how far they have moved and therefore what efforts should be put into the search effort."
Strong winds, cloud and rain had made searching difficult, said Kevin Short, air vice marshal at New Zealand's Defence Forces which sent a P-3K2 Orion to search the area on Thursday.
"The crew never found any object of significance," he told Radio New Zealand. "Visibility wasn't very good, which makes it harder to search the surface of the water," he said.
A nearby desolate group of French-administered sub-Antarctic islands including St Paul and Amsterdam and Kerguelen had been asked to look for debris, but none had been spotted, said Sebastien Mourot, chief of staff for the French prefect of La Reunion.
There have been many false leads and no confirmed wreckage found from Flight MH370 since it vanished off Malaysia's east coast, less than an hour after taking off.
There has also been criticism of the search operation and investigation, as more than two dozen countries scramble to overcome logistical and diplomatic hurdles to solve the mystery.
Investigators piecing together patchy data from military radar and satellites believe that, minutes after its identifying transponder was switched off as it crossed the Gulf of Thailand, the plane turned sharply west, re-crossing the Malay Peninsula and following an established route towards India.
What happened next is unclear, but faint electronic "pings" picked up by one commercial satellite suggest the aircraft flew on for at least six hours.
A source with direct knowledge of the situation said that information gleaned from the pings had been passed to investigators within a few days, but it took Malaysia more than a week to narrow the search area to two large arcs - one reaching south to near where the potential debris was spotted, and a second crossing to the north into China and central Asia.