NANNING — The core site of the recent plane crash in South China will be excavated as all-out efforts are made to continue searching for survivors and the second black box, officials said at a news briefing on March 25.

Field exploration and shallow surface excavation have been carried out at the core crash site in Guangxi Zhuang autonomous region, said Zhu Tao, head of the aviation safety office of the Civil Aviation Administration of China (CAAC).

Experts are working on an excavation plan for the core site, Zhu said, adding that DNA samples are being taken from relatives of the missing passengers.

The China Eastern Airlines Boeing 737 aircraft carrying 132 people crashed on the afternoon of March 21 in a mountainous area of Guangxi's Tengxian county. No survivors have been found so far. One black box has already been recovered.

The search and rescue scope has been expanded to nearly 200,000 square meters, and more than 2,200 people have joined the rescue efforts, said Lao Gaojin, vice-mayor of Wuzhou city that administers Tengxian.

As of 10 am on March 25, 531 family members of 92 missing passengers had arrived in Wuzhou.

The engine gearbox and main landing gear remnants were found in the core crash site, said Mao Yanfeng, head of the aviation accident investigation center of CAAC.

Mao noted that it is not certain when the downloading and analyses of data from the recovered black box will be completed.

A preliminary investigation report will be submitted to the International Civil Aviation Organization within 30 days in accordance with the Convention on International Civil Aviation, Mao added.