Satellite images of possible debris from the missing Malaysia Airlines flight MH370 have been released on a Chinese government website.
The three images show what appear to be large, floating objects in the South China Sea. Previous sightings of possible debris have proved fruitless.
Vietnam and Malaysia have sent planes to the area to investigate.
The Beijing-bound plane took off from Kuala Lumpur late on Friday, vanishing about an hour later.
No distress signal or message was sent from the plane, which had a total of 239 passengers and crew on board.
The three images are:
The images were taken on Sunday, a day after the plane disappeared, but were only released on Wednesday on the website of China's State Administration for Science.
China's civil aviation chief Li Jiaxiang said: "Chinese satellites have found smoke and floating objects... At present we cannot confirm this is related to the missing aircraft."
Vietnam's deputy transport minister said Vietnamese planes had already searched the area but would do so again.
Meanwhile, Malaysia's Transport Minister Hishammuddin Hussein said aircraft had been dispatched to the area to investigate.
Agence France-Presse quoted US officials as saying that US spy satellites had detected no sign of an explosion in the area at the time. The system has detected such heat signatures in the past but none was discovered this time, the officials said.
'All right, roger that'
On Thursday, Chinese Premier Li Keqiang urged Malaysia to step up the search.
"The Chinese government has asked the relevant party to enhance co-ordination, investigate the cause, locate the missing plane as quickly as possible and properly handle all related matters," he said.
China says it has deployed several warships, military aircraft and high-resolution satellites controlled from the Xian Satellite Control Centre in northern China to help search for the jet.
Earlier, Malaysian authorities revealed that the last communication from the jet suggested everything was normal on board.
Flight MH370 replied "All right, roger that" to a radio message from Malaysian air control, authorities said. Minutes later all contact with the plane was lost.
The area where the latest images were taken appears to be close to where the initial search took place.
Malaysian officials have since widened the search to the west of the peninsula amid reports that the plane could have tried to turn back or - for reasons that are not clear- turned west towards the Malacca Strait.
Malaysia said it had also asked India to join the search near the Andaman Sea, suggesting the plane might have reached those waters after crossing the Malacca Strait.
Earlier on Wednesday, Malaysia's air force chief Rodzali Daud denied remarks attributed to him in local media that the flight had been tracked by military radar to the Strait.
Gen Rodzali Daud said he "did not make any such statements", but added that the air force had "not ruled out the possibility of an air turn-back".
China's foreign ministry has complained that there is "too much confusion" regarding information released about the plane's flight path.
There were 153 Chinese nationals on the flight.
"It is very hard for us to decide whether a given piece of information is accurate," spokesman Qin Gang told reporters in Beijing.
Malaysian Transport Minister Hishammuddin Hussein dismissed the allegations and said that Malaysia would "never give up hope" of finding the plane's passengers and crew.
"It's only confusion if you want it to be seen as confusion," he told a press conference.
"I think it's not a matter of chaos. There are a lot of speculations that we have answered in the last few days," he added.