Indonesia AirAsia Flight QZ8501 lost contact with air traffic control in bad weather on Dec. 28, less than halfway into a two-hour flight from the Indonesian city of Surabaya to Singapore. None of the 162 people on the aircraft survived.
Searchers have also been hearing pings, believed to be from the aircraft's two black boxes near where the tail of the Airbus A320-200 aircraft tail was raised on Saturday.
Supriyadi, operations coordinator for the National Search and Rescue Agency, said on Sunday a sonar scan had revealed an object measuring 10 metres by four metres by 2.5 metres on the sea floor.
"They suspect it is the body of the plane. There is a big possibility that the black box is near the body of the plane," Supriyadi told Reuters in the town of Pangkalan Bun, the base for the search effort on Borneo.
"If it is the body of the plane then we will first evacuate the victims. Secondly we will search for the black box."
Forty-eight bodies have been found in the Java Sea off Borneo and searchers are still hunting for the plane's fuselage, which could contain more bodies.
Strong winds, currents and high waves have been hampering efforts to reach other large pieces of suspected wreckage detected by sonar on the sea floor.
Three vessels involved in the search have detected pings about 4 km (two miles) from where the plane's tail was raised on Saturday, in water about 30 metres (yards) deep.
"Three ships have (recorded) the pings so we can confirm the coordinates of the location of the black box," Indonesian National Transportation Safety Committee investigator Santoso Sayogo told Reuters.
If weather conditions are conducive, "hopefully they will recover the black box tomorrow morning," Santoso said. "The coordinates show the bottom of the sea (in that location) is sand so the divers should easily be able to see it."
If and when the recorders are found and taken to the capital, Jakarta, for analysis, it could take up to two weeks to download data, investigators said, although the information could be accessed in as little as two days if the devices are not badly damaged.
On Saturday, teams of divers in rubber dinghies battled the swell to attach inflatable balloons to the tail section, which was later hauled onto a rescue vessel and towed to Kumai Bay, not far from Pangkalan Bun, which has served as the base port for search and rescue vessels.
The aircraft carries cockpit voice and flight data recorders - or black boxes - near its tail but once the wreckage was visible, it quickly became apparent that the flight recorders were still underwater.
While the cause of the crash is not known, the national weather bureau has said seasonal storms were likely to be a factor.
President Joko Widodo, who took office in late October, said the AirAsia crash exposed widespread problems in the management of air transportation in Indonesia.
Separately on Sunday, a DHC-6 Twin Otter operated by Indonesia's Trigana Air crashed on landing at Enarotali Airport in Paniai, Papua, on Sunday.
Strong winds caused the aircraft to roll over, domestic news website Detik.com reported, with no injuries to the three crew members on board. The plane was not carrying any passengers.