Several objects and a body were seen floating in the Java Sea off the Indonesian part of Borneo, in one of the search zones for the plane.
An Indonesian official said the debris was 95% likely to be from AirAsia Flight QZ8501.
The Airbus A320-200, carrying 162 people from Surabaya in Indonesia to Singapore, disappeared on December 28.
The search operation is now in its third day, with the area widened to cover 13 zones over land and sea.
During a news conference by the head of the operation, pictures of the debris were shown, including a body floating on the water.
Relatives of passengers on the plane watching the pictures were visibly shocked.
Search operation head Bambang Soelistyo said he was 95% certain the objects shown were from the plane.
All resources were now being sent to the area where the debris was found, and all objects or bodies found will be taken to Pangkalan Bun, he said, referring to a nearby town in Central Kalimantan province.
Bambang Soelistyo added that ships with more sophisticated technology were being deployed to check whether larger parts of the plane were submerged beneath the debris.
Indonesian civil aviation chief Djoko Murjatmodjo, quoted by AFP news agency, said “significant things” such as a passenger door and cargo door had been found.
He added that the objects had been found 100 miles south-west of Pangkalan Bun.
At least 30 ships, 15 aircraft and seven helicopters joined the operation when it resumed at 06:00 local time on Tuesday, December 30.
The operation, led by Indonesia, includes assistance from Malaysia, Singapore and Australia, with other offers of help from South Korea, Thailand, China and France. The US destroyer USS Sampson is on its way to the zone.
Earlier, Indonesian officials said they were investigating reports of smoke seen rising from an island close to Belitung island, one of the focal points of the search, though experts cautioned it could be unrelated to the missing plane.
On board the plane were 137 adult passengers, 17 children and one infant, along with two pilots and five crew.
Most were Indonesian but the passengers included one UK national, a Malaysian, a Singaporean and three South Koreans.
The plane left Surabaya at 05:35 Jakarta time on December 28 and had been due to arrive in Singapore two hours later.
Safety officials say the captain had asked for permission to take the plane higher but, by the time permission was granted, communication with the plane was lost.
The plane was officially declared missing at 07:55.
AirAsia previously had an excellent safety record and there were no fatal accidents involving its aircraft.
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