The collapse of a bridge on an expressway in central China was likely caused by an explosion on a lorry carrying fireworks, a local official said Saturday as state media said the death toll rose to 11.

The accident on Friday sent an 80-metre (yard) stretch of viaduct crashing to the ground and left the twisted remains of cars and lorries scattered among the rubble, once again raising questions over the safety of China's infrastructure.

State television network CCTV said 11 people had been killed in the accident and four arrested because the lorry was not permitted to carry explosives.

An official with the Sanmenxia municipality's public security bureau named Zhang said rescuers using equipment to search for any more survivors had not detected any signs of life, warning that the toll could rise further.

"There are still vehicles buried in the rubble and we'll need heavy lifting equipment to get them out," he told AFP.

The municipality's deputy propaganda chief Ren Zhanzhou added that initial investigations suggested the lorry carrying firecrackers and fireworks ahead of the Lunar New Year holidays was the likely cause of the disaster.

Drivers interviewed by CCTV said they saw an explosion before the bridge collapsed, but on popular Internet forums, people were sceptical.

"Firecrackers and fireworks are not enough to destroy a bridge," one user identified as Xinghuhuhu wrote on Sina Weibo, the Chinese equivalent of Twitter.

"Have some respect for the dead, please! If a poor quality bridge is destroyed by firecrackers going off, it's not a question of a loss of face, some officials have to be fired," they added.

"There are times when you have to take responsibility."

State-run China National Radio initially said Friday that 26 people had been killed, but the report could not later be found on its website, after local authorities in Henan province called the figure "inexplicable".

Pictures of the accident showed tangled wreckage beneath the bridge, including three upturned lorries with their wheels pointing skywards, as rescue workers in orange uniforms scaled the wreckage.

A crowd of people peered at the debris through thick hazy fog as another lorry teetered on the mangled edge of the bridge's collapsed section.

A new bridge appeared to be under construction right next to the collapsed section.

The bridge near the city of Sanmenxia is on the G30 expressway, the longest road in China, which stretches for nearly 4,400 kilometres (2,700 miles) from China's western border with Kazakhstan to the eastern Yellow Sea.

It stands 30 metres above the ground, media reported.

Many of China's roads are packed as the country gears up for its most important holiday, the Lunar New Year, when hundreds of millions return to their hometowns in what is billed as the world's largest annual human migration.

The season is also a peak period for fireworks producers, as Chinese traditionally buy the explosives to celebrate the festival, which falls on February 10 this year.

According to police statistics, around 70,000 people die and 300,000 more are injured in road accidents every year in China, state media have reported.

China has seen a number of bridge collapses in recent years, which are often blamed on overloading and shoddy construction. One such incident in northeast China last August killed three people.