Photo taken on Dec. 30, 2014 shows Chinese rescue vessel Nanhaijiu 101 berthed in a port of Haikou, capital of south China's Hainan Province. [Photo/Xinhua]

The Chinese navy and air force are joining the search and rescue effort for the missing AirAsia plane.

The Chinese Defense Ministry says a frigate on routine patrol in the South China Sea is heading for the waters where the plane went missing.

Besides, Chinese patrol ship Haixun 31, rescue vessel Nanhaijiu 101 and Nanhaijiu 115 are also standing by.

An Air Force jet is also making preparations and coordinating with the countries on the flight route.

Indonesia is leading the search effort while Singapore, Malaysia, and Australia have contributed planes.

Earlier, the head of Indonesia's search-and-rescue agency said the missing jet with 162 people on board is believed to have sunk to the bottom of the sea.

Bambang Soelistyo said the hypothesis was based on the co-ordinates of the plane when contact with it was lost.

Indonesian Vice President Jusuf Kalla has vowed that his country will continue the search.

"There are 30 ship operation in the area and around 15 airplane and helicopters operating there. It is not easy of course in the operation in the sea, especially in the bad weather like this, but the President's instruction to all our people to do the best, and fast and (there is) no limit to find the plane and the passengers."