Jakarta: An object spotted during a sea search for an AirAsia plane was not from the aircraft, Indonesia's vice president said Monday, after reports that an Australian surveillance aircraft had found something.

"It has been checked and no sufficient evidence was found to confirm what was reported," Jusuf Kalla told a press conference at Surabaya airport from where the ill-fated plane departed.

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Kalla said there were 15 ships and 30 aircraft searching the area.

"It is not an easy operation in the sea, especially in bad weather like this," he said.

Indonesian Air Force spokesman Hadi Tjahjanto told AFP the search was now focused on a patch of oil spotted off Belitung island in the Java Sea.

Read: Missing AirAsia plane likely 'at bottom of sea': Indonesia search chief

"We are making sure whether it was avtur (aviation fuel) from the AirAsia plane or from a vessel because that location is a shipping line," he said.

Australia, Singapore and Malaysia have deployed planes and ships to assist in the Indonesian search for Flight QZ8501, which disappeared over the Java Sea on Sunday en route to Singapore.

Meanwhile, an Indonesian helicopter searching for the missing AirAsia jetliner saw two oily spots in the water Monday, and an Australian search plane spotted objects elsewhere in the Java Sea, but it was too early to know whether either was connected to the aircraft and its 162 passengers and crew.

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In any case, officials saw little reason to believe AirAsia Flight 8501 met anything but a grim fate after it disappeared from radar Sunday morning over the Java Sea. Wary of bad weather, one of the pilots had asked to raise the plane's altitude just before it vanished, but was not allowed because another aircraft was in the way.

"Based on the coordinates that we know, the evaluation would be that any estimated crash position is in the sea, and that the hypothesis is the plane is at the bottom of the sea," Indonesia search and rescue chief Henry Bambang Soelistyo said.