File photo of "South China Sea Rescue 101".[Photo/IC]

BEIJING - China said on Monday that it had sent aviation experts and a rescue vessel to join the Indonesian search operation for the black boxes from the ill-fated AirAsia Flight QZ8501.

Responding to a request from Indonesia, China sent an expert team to help in the search, the Civil Aviation Administration of China said in a statement on its website without elaborating.

In a separate statement, the Ministry of Transport said the rescue ship "South Sea Rescue 101", had left the city of Haikou and was expected to arrive at the search site on Jan 9.

Meanwhile, another vessel, "South Sea Rescue 115," is on standby, the ministry said.

The plane is believed to have crashed into the Java Sea on Dec 28 while en route from Surabaya of Indonesia to Singapore with 162 people on board. Weather could be behind the accident, as suggested by a preliminary analysis report by Indonesia's meteorological department.

Indonesia's search and rescue teams had located a fifth large object on the seabed by Sunday, but the black boxes remain unaccounted for.