The latest sighting followed reports by an Australian crew over the weekend of a floating wooden pallet and strapping belts in an area of the icy southern Indian Ocean that was identified after satellites recorded images of potential debris.
Flight MH370 vanished from civilian radar screens less than an hour after taking off from Kuala Lumpur for Beijing with 239 people on board on March 8. No confirmed sighting of the plane has been made since and there is no clue what went wrong.
Attention and resources in the search for the Boeing 777 have shifted from an initial focus north of the equator to an increasingly narrowed stretch of rough sea in the southern Indian Ocean, thousands of miles from the plane's original flight path.
The Australian Maritime Safety Authority (AMSA) said it had been advised of the Chinese sighting and will use other aircraft scheduled to search the area on Monday to relocate the objects.
The Chinese Ilyushin IL-76 aircraft spotted two "relatively big" floating objects and several smaller white ones dispersed over several kilometres, the Xinhua news agency said.
China has diverted its icebreaker Xuelong, or Snow Dragon, toward the location where the debris was spotted, Xinhua said. A flotilla of other Chinese ships are also steadily making their way south. Over 150 of the passengers on board the missing plane were Chinese.
In a further sign the search may be bearing fruit, the United States Navy is flying in its high-tech Black Box detector to the area.
The so-called black boxes - the cockpit voice recorder and flight data recorder - record what happens on board planes in flight. At crash sites, finding the black boxes soon is crucial because the locator beacons they carry fade out after 30 days.
"If debris is found we will be able to respond as quickly as possible since the battery life of the black box's pinger is limited," Commander Chris Budde, U.S. Seventh Fleet Operations Officer, said in an emailed statement.
Budde stressed that bringing in the black box detector, which is towed behind a vessel at slow speeds and can pick up "pings" from a black box to a maximum depth of 20,000 feet, was a precautionary measure.
The Chinese aircraft that spotted the objects was one of two IL-76s searching early on Monday. Another eight aircraft, from New Zealand, Australia, the United States and Japan, were scheduled to make flights throughout the day to the search site, some 2,500 km (1,550 miles) southwest of Perth.
WEATHER MAY DETERIORATE
Aircraft flying on Monday were focused on searching by sight, rather than radar, which can be tricky to use because of the high seas and wind in the area.
"It's a lot of water to look for just perhaps a tiny object," Australian Deputy Prime Minister Warren Truss told Australian Broadcasting Corp. Radio before the Chinese report.
"Today we expect the weather to deteriorate and the forecast ahead is not that good, so it's going to be a challenge, but we will stick at it," he said.
Australia was also analysing French radar images showing potential floating debris that were taken some 850 kms (530 miles) north of the current search area.
"We only recently got this information and we are still examining it," an AMSA spokeswoman told Reuters by telephone. Malaysia said it received the images on Sunday and passed them on to Australia.
Australia has used a U.S. satellite image of two floating objects to frame its search area. A Chinese satellite has also spotted an object floating in the ocean there, estimated at 22 metres long (74ft) and 13 metres (43ft) wide.
It could not be determined easily from the blurred images whether the objects were the same as those detected by the Australian and Chinese search planes, but the Chinese photograph could depict a cluster of smaller objects, said a senior military officer from one of the 26 nations involved in the search.
The wing of a Boeing 777-200ER is approximately 27 metres long and 14 metres wide at its base, according to estimates derived from publicly available scale drawings. Its fuselage is 63.7 metres long by 6.2 metres wide.
NASA said it would use high-resolution cameras aboard satellites and the International Space Station to look for possible crash sites in the Indian Ocean. The U.S. space agency is also examining archived images collected by instruments on its Terra and Aqua environmental satellites, said NASA spokesman Allard Beutel.
SOMEONE ON BOARD
Investigators believe someone on the flight shut off the plane's communications systems. Partial military radar tracking showed it turning west and re-crossing the Malay Peninsula, apparently under the control of a skilled pilot.
That has led them to focus on hijacking or sabotage, but investigators have not ruled out technical problems. Faint electronic "pings" detected by a commercial satellite suggested it flew for another six hours or so, but could do no better than place its final signal on one of two vast arcs north and south.
The lack of solid news has meant a prolonged and harrowing wait for families of the passengers, who have complained in both Beijing and Kuala Lumpur about the absence of information.
A Malaysian statement said a "high-level" team briefed relatives in Beijing on Sunday in a meeting that lasted more than six hours.
While the southern arc is now the main focus of the search, Malaysia says efforts will continue in both corridors until confirmed debris are found.
"We still don't even know for certain if the aircraft is in this area," Truss said earlier on Monday of the southern Indian Ocean search.
"We're just clutching at whatever little piece of information that comes along to try to find the place we can concentrate the efforts."