A China Eastern Airlines Boeing 737-800 with 132 people on board crashed in mountains in southern China on Monday after a sudden descent from cruising altitude.
Media reports say there were no signs of survivors.
The airline said it deeply mourned the passengers and crew, without specifying how many people had been killed.
Chinese media showed brief highway video footage from a vehicle's dashcam apparently showing a jet diving to the ground behind trees at an angle of about 35 degrees off vertical.
Reuters could not immediately verify the footage.
A graphic showing the last known position of the China Eastern passenger jet. Source: SBS News
The People's Daily quoted a provincial firefighting department official as saying there was no sign of life among the debris.
State media showed a piece of the plane on a scarred, earthen hillside.
There was no sign of a fire or personal belongings.
The aircraft, with 123 passengers and nine crew on board, lost contact over the city of Wuzhou, China's Civil Aviation Administration of China (CAAC) and the airline said.
Flightradar24 indicated the plane was six years old.
Crashes during the cruise phase of flights are relatively rare even though this phase accounts for the majority of flight time.
Boeing said last year only 13 per cent of fatal commercial accidents globally between 2011 and 2020 occurred during the cruise phase, whereas 28 per cent occurred on final approach and 26 per cent on landing.
"Usually the plane is on auto-pilot during cruise stage. So it is very hard to fathom what happened," said Li Xiaojin, a Chinese aviation expert.
Online weather data showed partly cloudy conditions with good visibility in Wuzhou at the time of the crash.
President Xi Jinping called for investigators to determine the cause of the crash as soon as possible, state broadcaster CCTV reported.
A Boeing spokesperson said: "We are aware of the initial media reports and are working to gather more information."
Shares of Boeing Co were down five per cent on Monday.
Shares in China Eastern Airlines in Hong Kong closed down 6.5 per cent after news of the crash emerged, while its US-listed shares slumped 17 per cent in pre-market trading.
China Eastern grounded its fleet of 737-800 planes after the crash, state media reported.
China Eastern has 109 of the aircraft in its fleet, according to FlightRadar24.
Aviation data provider OAG said this month that state-owned China Eastern Airlines was the world's sixth-largest carrier by scheduled weekly seat capacity.
The 737-800 has a good safety record and is the predecessor to the 737 MAX model that has been grounded in China for more than three years after fatal crashes in Indonesia and Ethiopia.
China's airline safety record has been among the best in the world for a decade.
"The CAAC has very rigid safety regulations and we will just need to wait for more details," said Shukor Yusof, head of Malaysia-based aviation consultancy Endau Analytics.
Investigators will search for the plane's black boxes - the flight data recorder and cockpit voice recorder - to shed light on the crash.
According to Aviation Safety Network, China's last fatal jet accident was in 2010, when 44 of 96 people on board were killed when an Embraer E-190 regional jet flown by Henan Airlines crashed on approach to Yichun airport.
