At least 19 people died when part of a highway collapsed due to heavy rains in southern China's Guangdong province on Wednesday, state media said.

State broadcaster CCTV said a stretch of road between Meizhou city and Dabu county in Guangdong province caved in at around 2:10 am (1810 GMT Tuesday).

The incident caused 18 vehicles to become trapped and involved a total of 49 people, CCTV said.

As of 11:45 am, "19 people have been confirmed dead, and 30 are receiving all-out emergency care in hospital", according to the broadcaster.

It added that the lives of those hospitalised were "not currently at risk" but did not specify what their injuries were.

An aerial photograph published by CCTV showed wrecked vehicles lying in a deep muddy pit where the highway once ran.

Dozens of emergency vehicles and cranes congregated along the intact section of the road, which bisects a steep, wooded slope.

Other clips apparently filmed before dawn showed flames emanating from the pit.

"You can't go any further," a man is heard saying in one video, adding parts of the road had given way.

AFP was not immediately able to verify the videos.

CCTV said the collapse was a "natural geological disaster... (that occurred) under the impact of persistent heavy rain."

It reported that a nearly 18-metre (59-foot) stretch of road had fallen away.

Authorities have dispatched around 500 people to the site to help with the rescue operation, CCTV reported.

They are drawn from departments handling public security, emergency response, firefighting and mining rescue, according to the broadcaster.

Local authorities said in a notice that part of the S12 highway was closed in both directions and ordered drivers to take detours.

The incident is the latest in a string of deadly disasters to hit Guangdong in recent weeks.

The province -- a densely populated industrial powerhouse -- has been lashed by heavy rains that have caused fatal floods in some areas.

A swirling tornado killed five people when it ripped through the megacity of Guangzhou last week.

Much of China's massive highway network sprawls across rough terrain and extreme climates.

Road accidents are also common in the country due to a lack of strict safety controls.

In March, 14 people were killed and 37 others injured after a bus crashed inside an expressway tunnel in northern Shanxi province.

And sixteen died in a vehicle pile-up in central Hunan province in February last year, a month after 19 perished in an accident in eastern Jiangxi province.

Parts of the province have not seen such severe flooding so early in the year since records began in 1954, according to state media reports.

Climate change driven by human-emitted greenhouse gases makes extreme weather events more frequent and intense, and China is the world's biggest emitter.

China is the biggest emitter of the greenhouse gases that contribute to climate change but has pledged to reduce emissions to net zero by 2060.