Rescuers in southern China searched for survivors from a China Eastern Airlines jet on Tuesday after it crashed with 132 people on board and authorities said severe damage to the aircraft would make it difficult to establish the cause of the crash.

Flight MU5735 was headed on Monday for the port city of Guangzhou from Kunming, capital of the southwestern province of Yunnan, when it plunged from cruising altitude to crash in the mountains of Guangxi less than an hour before landing time.

A jet appeared to dive to the ground at an angle of about 35 degrees from the vertical in video images from a vehicle’s dashboard camera, according to Chinese media.

No survivors have been found yet, said Zhu Tao, director of aviation safety at the Civil Aviation Administration of China, told reporters.

“The jet was seriously damaged during the crash, and investigations will face a very high level of difficulty,” Zhu said at the first government briefing on the disaster.

“Given the information currently available, we still do not have a clear assessment of the cause for the crash,” he said, adding that the aircraft did not respond to repeated calls from air controllers during its rapid descent.