Sonar scans have detected a large, dark object beneath the sea near where debris and bodies were found on the surface.
Flight QZ8501, carrying 162 passengers, went missing on Sunday after losing contact during bad weather about 40 minutes into its flight from the Indonesian city of Surabaya to Singapore.
Dozens of bodies have been spotted in the sea and seven have been recovered, some fully clothed, which could indicate the Airbus A320-200 was intact when it hit the water.
The discovery could support a theory that it suffered an aerodynamic stall in mid-air.
One of the recovered bodies was initially reported to have been wearing a life jacket.
But the Indonesian official who earlier gave that information later retracted it, saying there was a time difference of about two hours between the discovery of a body and a life jacket.
Most of those on board were Indonesians. No survivors have been found.
Did the plane stall?
Discussion among pilots in online forums has centred on unconfirmed secondary radar data from Malaysia that suggested the aircraft was climbing at a speed of 353 knots, about 100 knots too slow – and that it might have stalled.
Investigators are reportedly looking into whether the crew took too long to request permission to climb, or could have climbed on their own initiative earlier.
Authorities in Surabaya were preparing to receive and identify bodies, gathering 130 ambulances to take victims to a police hospital and collecting DNA from relatives.
Strong wind and waves hampered the search and with visibility at less than half a mile, the air operation was called off in the afternoon.
Indonesian President Joko Widodo said his priority was retrieving the bodies.