Chinese state television says the plane, flying from Kunming to Guangzhou, had an “accident” over Guangxi.
The China Eastern Airlines flight had 133 passengers on board at the time of the incident.
It is unknown how many casualties there are but rescue is said to have been sent to the mountainous region.
Firefighters who first reached the scene had already extinguished the blaze in the hills caused by the plane crash, CCTV reported. The Guangxi Emergency Management Department said in a statement:
A Boeing 737 passenger plane carrying 133 people from China Eastern Airlines crashed in Teng County, Wuzhou, Guangxi, and caused a mountain fire.
At present, rescue teams have assembled and approached, and the casualties are unknown.
A video shared online showed white smoke billowing from between trees.
We are following multiple unconfirmed reports about a possible accident involving China Eastern Airlines flight #MU5735 a Boeing 737-89P (B-1791) en route from Kunming to Guanghzou, China.
Flight data claimed to be from the flight shows the plane dropped from 24 000 to the ground in just minutes, giving the crew little time to react to whatever the issue was.