JAKARTA/PANGKALPINANG, Indonesia, Dec. 29-- Suspicious objects were detected on Monday in the Java Sea where an AirAsia plane disappeared as the search operation expanded with more countries joining the sea and aerial hunt.

Indonesian Vice President Jusuf Kalla told a press conference at Surabaya airport that he received reports that an Australian Orion surveillance plane had spotted suspicious objects near the Nangka Island, 1,120 km from the location where the jetliner lost contact.

However, the vice president said he could not confirm whether the objects were parts of the missing QZ8501 flight.

They "have not been clarified," he said, adding that rescuers and searchers were verifying the reports.

Meanwhile, Air Force spokesman Hadi Tjahnanto said an Indonesian helicopter had spotted an oil slick some 100 nautical miles (185 km) off the east coast of the Belitung Island.

"We haven't been able to confirm, however, whether it was the fuel of the AirAsia aircraft," he said.

Earlier, an Indonesian official told the media that the missing jet with 162 people on board was believed to have sunken into the bottom of the sea.

"Because the coordinate that was given to us and the evolution from the calculation point of the flight track is at sea, our early conjecture is that the plane is at the bottom of the sea," said Bambang Sulistyo, head of the National Search and Rescue Agency (Basarnas).

Should the projection be true, Indonesia needed to cooperate with other countries to bring the wreckage to the surface, he added.

The Airbus A320-200 disappeared Sunday en route from Surabaya in Indonesia's East Java to Singapore after the pilot requested a change of flight plan due to stormy weather.

The flight lost contact with the ground after the air traffic control consented to the pilot's request to change flight route but it did not approve the request to raise its height of flight to 34,000 feet (10,303 meters).

The aircraft, which sent no distress signal, must have run out its fuel if it kept flying. said Djoko Murjatmodjo, director general of air transport of the Indonesian Transport Ministry.

Aircraft and ships from Singapore, Malaysia and Australia have been deployed to assist Indonesia's search efforts, which is centered on waters around the Belitung Island in the Java Sea across from Kalimantan on the Borneo Island.

Sutono, a spokesman at the search and rescue command at the Pangkalpinang airport, said on Monday, "Indonesia engages six vessels from Basarnas, the Navy and the fishery and maritime ministry. From the air, Indonesia dispatches four helicopters and 15 fixed-wing planes."

"Singapore and Malaysia sent C-130 Hercules planes each. Meanwhile Australia sent two maritime patrol planes AP-3C Orion," he told Xinhua.

Areas combed by those planes and vessels were focused on five points in a large quadrant square perspective map that spans to the Indonesian waters near Singapore, he said.

According to AirAsia, a Malaysia-based budget airline, 155 of those on board flight QZ8501 were Indonesians, with three South Koreans and one person each from Singapore, Malaysia, Britain and France, including 16 children and an infant.

The ill-fated plane vanished from the radar screen at 6:17 a.m. local time Sunday (23:17 GMT Saturday), 42 minutes after it took off from Surabaya in Indonesia's East Java province.

After Sunday's mishap, the Indonesian government vowed to check the safety standard of all AirAsia planes operating in Indonesia.

"We will carry out ramp checks, and also review operation of AirAsia in Indonesia to convince customers that all the activities will be better in the future," Transport Minister Ignasius Jonan told a press conference at the Jakarta airport.

The incident is possibly the third Malaysia-linked air disaster this year. Malaysia Airlines Flight MH370, a Boeing 777 with 239 people on board, disappeared on March 8 after diverting from its Kuala Lumpur-Beijing course. No traces of the jetliner have been found despite massive search efforts.

Months later, MH17, also a Boeing 777, went down on July 17 in the war-torn eastern Ukraine en route from Amsterdam to Kuala Lumpur, killing all 298 aboard.

AirAsia, a low-cost carrier established in 2001, has dominated cheap traveling in the region for years with about 100 destinations and affiliate companies in several Asian countries.