State broadcaster CCTV reported a 17.9-metre (58.7-foot) stretch of the S12 highway between Meizhou city and Dabu county caved in at about 2:10am on Wednesday (18:10 GMT on Tuesday), trapping dozens of people in their vehicles.
CCTV had earlier reported that 19 people had been confirmed dead. It added that 30 were receiving emergency care in hospital.
The lives of those in hospital were “not currently at risk,” it added but did not go into detail on the injuries.
Social media footage shared by local news outlets showed flames and smoke rising from a deep, dark pit into which the cars appeared to have fallen.
Authorities have sent about 500 people to the site to help with the rescue operation, CCTV reported.
The cause of the collapse was not specified.
Guangdong has been hit by a series of extreme weather events in recent weeks, from heavy rain to flooding and a deadly tornado.
MNA/PR