A truck carrying fireworks has exploded on a highway bridge in central China, killing at least five people as it sent vehicles plunging 30 metres to the ground.

The blast, which took place around 8.52am local time, destroyed an 80-metre-long section of the bridge, the official Xinhua news agency said.

Six vehicles have been retrieved from the debris, and eight people were injured, Xinhua added.

State television CCTV carried footage showing rescuers digging through debris for survivors.

CCTV said more than 10 trucks were found crashed under the bridge, and 15 people had been rescued.

The report did not give details on the condition of those rescued.

Rescue efforts were still underway, with authorities investigating the cause of the accident, CCTV said.