JAKARTA/PANGKALPINANG, Indonesia, Dec. 30 -- More countries were sending planes and ships on Tuesday to join an expanding search operation in the Java Sea off Indonesia where an AirAsia plane disappeared as the sea and aerial hunt entered its third day.

Around 30 ships, 15 fixed-wing aircraft and seven helicopters from Indonesia, Malaysia, Singapore and Australia had been scouring the missing flight QZ8501 in some 10,000 square nautical miles on Tuesday, said Bambang Sulistyo, head of the National Search and Rescue Agency.

He told a local TV that the search would be expanded to land areas with helicopters beginning to comb land on Kalimantan as well as islands in the area. So far the search has been focused on the Java Sea between the islands of Sumatra and Borneo.

Meanwhile, more countries were joining the international search efforts for the Airbus A320-200, which was flying from Surabaya in Indonesia's East Java province to Singapore on Sunday with 162 people aboard.

China said on Monday it would send a warship and an Air Force jet to help look for the missing AirAsia plane.

A Navy frigate on a routine patrol in the South China Sea was heading to the waters where flight QZ8501 went missing, the Defense Ministry said in a statement.

An Air Force plane was making preparations and coordinating with the countries on the flight route, it added.

South Korea was also sending a surveillance plane to join the Indonesia-led search operation.

Seoul's Foreign Ministry said it would dispatch the aircraft as early as late Tuesday and it had been in talks with six countries to get approval for the plane to pass their airspace.

The U.S. Navy was also joining the search. It said in a statement that the USS Sampson, a guided missile destroyer which was already on an independent deployment in the Western Pacific, would arrive in the area later Tuesday.

Aircraft from Thailand also planned to join the search on Tuesday.

Although no significant clues or wreckage were found over the past two days, the Indonesian authorities said on Monday that they would check an oil slick spotted some 100 nautical miles (185 km) off the east coast of Belitung island.

"We haven't been able to confirm, however, whether it was the fuel of the AirAsia aircraft," Air Force spokesman Hadi Tjahnanto said.

The AirAsia flight vanished from the radar screen at 6:17 a.m. local time Sunday (2317 GMT Saturday), 42 minutes after it took off from Surabaya.

The ill-fated plane lost contact with ground after the air traffic control consented to the pilot's request to change flight route due to a cloudy condition, but it did not approve his 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.

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

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.