The number of casualties and reason for the crash are not yet known.
The crash of the Boeing 737 jet, in a mountainous region, led to a fire in the woods, state media is reporting.
Flight MU5735 was scheduled to leave Kunming at 13:15 local time (05:15 GMT) and was en route to Guangzhou.
Flight tracking sites report the plane was in the air for just over an hour.
The plane went down near Teng county in Wuzhou province. Guangxi is a southern province neighbouring Guangzhou, a major city in the south-east.
Rescue crews have been deployed to the area, CCTV reported.
According to FlightRadar23 data, the last sourced information on the flight showed it ended at 14:22 local time, at an altitude of 3,225 ft.