Over a day after a passenger aircraft with 132 people on board crashed in a mountainous area in south China, a Chinese official said on Tuesday that no survivors have been found, official media here reported.

No survivors have been found so far in Monday's plane crash, said Sun Shiying, chairman of China Eastern Airlines Yunnan branch.

The announcement of no survivors came as hundreds of rescuers carried out desperate search operations in the mountainous regions where the Boeing 737, on its way from the Chinese city of Kunming to Guangzhou, plunged and crashed.

An all-out search operation for the black boxes of the crashed passenger plane was underway, Sun said in his first media briefing on the plane crash in Nanning, capital of Guangxi province from where most of the rescue operations are being directed.

Contacts have been made with families of all 123 passengers, Sun was quoted as saying by state-run Xinhua news agency.

Based on known information, the authorities do not yet have a clear clue to the cause of the passenger plane crash, an aviation official said.

The cause of the crash cannot be confirmed immediately and the investigation into the cause is difficult, said Zhu Tao, an official with the Civil Aviation Administration of China (CAAC).

Aircraft debris and some personal belongings have been found at the air crash site in Tengxian County of Wuzhou City, south China's Guangxi Zhuang Autonomous Region, official media reported.

People on-board the aircraft are still unaccounted for as the rescue work is underway at the mountainous site, the state television reported over 24 hours after China's worst air disaster in over a decade.

Aircraft debris and some personal belongings have been found at the air crash site in Tengxian County of Wuzhou City, but no survivors, state-run CGTN reported.

Answering questions about the rescue efforts, Chinese Foreign Ministry spokesperson Wang Wenbin told reporters in Beijing on Tuesday that he is deeply grieved by the China Eastern Airlines passenger plane crash, adding that search and rescue missions are underway to find out the cause of the incident as soon as possible.

Meanwhile, rescue work continued on Tuesday night with over 2,000 people involved in the search operations.

The Chinese military has deployed drones to conduct search operations. A whole lot of machinery, including excavators, have been moved into the mountainous forest area where the crash has occurred.

"The site of the crash in a mountain forest complicates the search for the black boxes and we have to rely mainly on drones and rescue staff, Zhu Xiaodong, a rescuer, told official media.

Experts from the public security department and the Civil Aviation Administration of China (CAAC) are entering the main crash site to search for physical evidence, confirm the identity of the missing persons and find out the possible cause of the accident.

Some personal belongings of the passengers have been collected and numbered.

Drones have been deployed to search for more evidence in an area of nearly 680,000 square meters, said Zhang Xueliang, another rescuer.

"The drones' thermal imaging function will help locate the black boxes," Zhang said. At around 7:30 a.m. on Tuesday, light rain began to fall over the rescue site.

The local meteorological department forecast that more rain and high winds would hit the area in the next 24 hours, which might adversely affect the search efforts.

At night, rescuers used searchlights to carry out the operations. On Tuesday, around six excavators and nearly 50 workers scrambled to clear a passage to the site for the rescue crew and the necessary machinery.

"We need to complete all preparations prior to the rain, and the initial objective is to gain entry to the site by approximately 8 p.m. Tuesday," Guo Zhaoliang, in charge of the route construction, said.

Many nearby residents have volunteered to deliver tents, food and other relief supplies to the site by motorcycle.

The China Eastern Airlines Boeing 737 aircraft, which departed from Kunming and was bound for Guangzhou, crashed into a mountainous area in Tengxian County in Guangxi at 2:38 p.m. on Monday, causing a mountain fire.

China's civil aviation regulator has called for screening hidden risks to boost civil aviation safety.

Concrete measures should be taken to strengthen the investigation of hidden dangers concerning aircraft maintenance, flight weather conditions, personnel qualifications and operational skills, said the CAAC.

On Tuesday, Boeing China said that it is cooperating with China Eastern Airlines, and its technical experts are ready to aid the CAAC in conducting the investigation.