NANNING -- The emergency response headquarters' major search and rescue operation for the recent plane crash of China Eastern Airlines has been basically completed, an official said on Thursday.

All emergency response commanders and on-site search and rescue personnel completed the search for the two black boxes of the passenger plane in seven days, while finishing the identification and DNA testing of all the passengers in eight days, Zhu Tao, head of the aviation safety office of the Civil Aviation Administration of China, told a press briefing on Thursday.

A total of 49,117 pieces of wreckage had been recovered as of 4 pm Wednesday after a core area covering over 400,000 square meters was searched and 22,700 cubic meters of earth were excavated, said Zhang Zhiwen, an official with the government of South China's Guangxi Zhuang autonomous region.

Zhu said preliminary analysis is being carried out now that the site, debris distribution and impact marks have been located and photographed.

He added the data of the black boxes are also being decoded.

The emergency response headquarters had conducted over 7,900 psychological evaluations and provided over 2,900 psychological counseling sessions by Wednesday, according to the press briefing.

A preliminary investigation report on the plane crash is expected to be completed within 30 days of the incident, and a complete report will be released to the public after all investigations are finished, according to Zhu.

"We will leave no stone unturned to find out the cause of the accident and prevent similar accidents from happening again," Zhu said.

A Boeing 737 airplane, which departed from Kunming, capital of Southwest China's Yunnan province, and was bound for Guangzhou, capital of Guangdong province, crashed into a mountainous area in Tengxian county, Guangxi, at around 2:38 pm on March 21. All 132 people on board the plane were killed.