Satellite images on a Chinese government website show suspected debris from the missing Malaysia Airlines plane floating off the southern tip of Vietnam, China's Xinhua News Agency says.
The revelation could provide searchers with a focus that has eluded them since the plane disappeared with 239 people aboard early on Saturday.
The Xinhua report said the images from around 11am on Sunday appear to show "three suspected floating objects" of varying sizes, the largest about 79ft by 72ft.
The report includes co-ordinates of a location in the sea off the southern tip of Vietnam and east of Malaysia, near the plane's original flight path. The images were originally posted on a national defence technology website.
No other governments have confirmed the Xinhua report, which did not say when Chinese officials became aware of the images and associated them with the missing plane.
The search for the plane, which left Kuala Lumpur for Beijing before disappearing, has encompassed 35,800 square miles of south-east Asia and has expanded toward India.
Two-thirds of the passengers on the flight were Chinese, and the Beijing government has put increasing pressure on Malaysian officials to solve the mystery of the plane's disappearance.
Earlier today it was revealed that the last message from the cockpit of the missing flight was routine. "All right, good night," was the sign-off transmitted to air traffic controllers five days ago.
Then the Boeing 777 vanished as it cruised over the South China Sea toward Vietnam, and nothing has been seen or heard of it since.
Those final words were picked up by controllers and relayed in Beijing to anguished relatives of some of the people aboard Flight MH370.
The new Chinese reports of the satellite images came after several days of sometimes confusing and conflicting statements from Malaysian officials.
The Malaysian military earlier officially disclosed why it was searching on both sides of country: A review of military radar records showed what might have been the plane turning back and crossing westward into the Strait of Malacca.
That would conflict with the latest images on the Chinese website.
For now, authorities said the international search effort would stay focused on the South China Sea and the strait leading toward the Andaman Sea.
Chinese foreign ministry spokesman Qin Gang said: "There's too much information and confusion right now. It is very hard for us to decide whether a given piece of information is accurate. We will not give it up as long as there's still a shred of hope."
"We have nothing to hide," said Malaysian defence minister Hishammuddin Hussein. "There is only confusion if you want to see confusion."
Flight MH370 disappeared from civilian radar screens at 1.30am on Saturday at an altitude of about 35,000ft above the Gulf of Thailand between Malaysia and southern Vietnam. It sent no distress signals or any indication it was experiencing problems.
The amount of time needed to find aircraft that go down over the ocean can vary widely. Planes that crash into relatively shallow areas, like the waters off Vietnam where the Malaysian jet is missing, are far easier to locate and recover than those that plunge deep into undersea canyons or mountain ranges.
By contrast, much of the Gulf of Thailand is less than 300ft deep.
The Malaysian government said it had asked India to join the search near the Andaman Sea, suggesting the jetliner might have reached those waters after crossing into the Strait of Malacca, 250 miles from the flight's last-known co-ordinates.
Malaysian officials met several hundred Chinese relatives of passengers in Beijing to explain the search and investigation, and to relay the last transmission that Malaysian air traffic controllers received before the plane entered Vietnamese air space, according to a participant in the meeting.
Aviation officials in Vietnam said they never heard from the plane.
Its sudden disappearance led to initial speculation of a catastrophic incident that caused it to disintegrate. Another possibility is that it continued to fly despite a failure of its electrical systems, which could have knocked out communications, including transponders that enable the plane to be identified by commercial radar.
Authorities have not ruled out any possible cause, including mechanical failure, pilot error, sabotage and terrorism, and they are waiting to find any wreckage or debris to determine what went wrong.
In June last year, Boeing issued a safety alert to Boeing 777 operators, telling them to inspect for corrosion and cracks in the crown fuselage around a satellite antenna. The alert says one airline found a 16in crack in one plane, then checked other 777s and found more cracking.
Confusion over whether the plane had been seen flying west prompted speculation that different arms of the government might have different opinions about its location, or even that authorities were holding back information.
Earlier in the week, Malaysia's head of civil aviation, Azharuddin Abdul Rahman, was asked why the Strait of Malacca was being searched and replied: "There are things I can tell you, and things I can't," suggesting that the government was not being completely transparent.
If all those on board are confirmed dead, it would be the deadliest commercial air accident in 10 years.