The Indonesian search and rescue team has found two big objects, which have been confirmed to be part of the wreckage of the downed AirAsia QZ8501, on the ocean floor.

Search and rescue agency chief Fransiskus Bambang Soelistyo told reporters in a news conference at Jakarta that the two objects were found just before midnight on 2 January around 30 metres underwater in Java Sea.

A piece of the plane's fuselage had been found earlier on the same day.

The agency is using remotely operated underwater vehicles (ROV) to get images of the objects, which are measuring 9.4 metres by 4.8 metres by 0.4 metres, and 7.2 metres by 0.5 metres, he added.

"We have detected two objects underwater (at) 30 metres depth," said Soelistyo.

"With the discovery of an oil spill and two big parts of the aircraft, I can assure you these are the parts of the AirAsia plane we have been looking for."

"As I speak we are lowering an ROV to get an actual picture of the objects detected on the sea floor. All are at the depth of 30 metres."

Soelistyo noted that large waves in the area made it difficult to operate ROVs, adding that divers were preparing to search for the objects.

The agency earlier said it had widened the search area on 3 January as debris may have drifted more than 200 nautical miles.

AirAsia plane QZ8501, an Airbus A320, had earlier disappeared with 162 people on board while flying from Surabaya in Indonesia to Singapore.

The search and rescue teams have so far discovered 30 bodies, and operations to recover victims are continuing. The cause of the crash is not known yet.

The plane was flying at 32,000 feet and the pilot had asked to raise the elevation to 38,000 feet to avoid bad weather just before contact was lost.