Rescuers in China are scouring heavily forested slopes in southern China where a China Eastern Airlines crashed and exploded in flames, as the airline expressed “deep condolences” for those on board.

Some 132 people, including nine crew, were on flight MU5735 when it crashed in the mountains of southern Guangxi on a flight from Kunming to Guangzhou.

The Boeing 737-800 crash is the first involving a commercial aircraft in China since 2010.

Debris was strewn across mountain slopes with state media reporting that the burned remains of identity cards, purses, and wallets had been seen.

“The company expresses its deep condolences for the passengers and crew members who died in the plane crash,” China Eastern said in a statement, without providing more information.

The plane was flying at a cruising altitude when it suddenly plunged from the sky.

Flight tracking website FlightRadar24 showed the aircraft dropped from an altitude of 29,100 feet (8,870 metres) to 7,850 feet (2,393 metres) in just over a minute.

After a brief upswing, it then plunged to 3,225 feet (982 metres), the tracker said.

Chinese media carried brief highway video footage from a vehicle’s dashcam showing a jet diving to the ground behind trees at an angle of about 35 degrees off vertical. The footage could not immediately be verified.

“The plane fell vertically from the sky,” state-run Beijing Youth Daily quoted a resident as saying.

“Although I was far away, I could still see that it was a plane. The plane did not emit smoke during the fall. It fell into the mountains and started a fire.”

‘Complex emotions’

State media have described the situation as appearing “grim” with hundreds of firefighters and paramilitary forces, some with dogs, deployed to the scene. Local villagers also rushed to help after seeing the flames.

Describing the difficult terrain, state media said the crash site was hemmed in by mountains on three sides, with access provided by a single, tiny path. Rain is forecast for the area this week.

The last crash of a commercial aircraft in mainland China was in 2010, when an Embraer E-190 regional jet flown by Henan Airlines crashed on approach to Yichun airport in low visibility, killing 44 of 96 people on board.

Accidents typically involve multiple factors, and experts said it was too early to draw conclusions on the potential causes of Monday afternoon’s crash.

Hassan Shahidi, president and CEO of the Flight Safety Foundation said accidents at cruising altitude were “certainly rare” whether in China or elsewhere.

“The investigators will be looking at all aspects of this flight, including any mechanical, or structural issues,” Hassan told Al Jazeera in an email. “They will be looking into the maintenance history of the aircraft as well as records of pilot training. Boeing is expected to be part of the process to provide the necessary expertise.  Investigators would want to find the flight data recorder and the voice recorder to find out exactly what happened.”

Chinese President Xi Jinping has called for a full investigation into the crash.

China Eastern on Monday grounded its fleet of 737-800 planes, state media reported. It has 109 of the aircraft, according to FlightRadar24.

Boeing Chief Executive Dave Calhoun told employees that the manufacturer had offered the full support of its technical experts in the crash investigation.

“Trust that we will be doing everything we can to support our customer and the accident investigation during this difficult time, guided by our commitment to safety, transparency, and integrity at every step,” Calhoun said in an email to employees.

China Eastern is one of the country’s three major airlines and operates dozens of domestic and international routes.

The airline changed its website to black and white after the crash and has opened an emergency assistance phone number for the families of those on board. At Guangzhou airport, staff in full personal protective equipment held up signs to direct distraught relatives to a waiting area marked by high black screens emblazoned with the word “emergency” and guarded by officials and police.

One airport staffer told the AFP news agency her colleagues were “focusing on taking care” of the relatives of those involved in the crash.

A man surnamed Ye told the news agency his colleague Tan was on the plane.

“When we heard the news… [we] called him over and over for hours, but never got through,” Ye said, adding he had alerted the man’s parents, who were “going through some very complex emotions”.