Safety violations on a vehicle unloading explosives have been cited following a deadly tunnel blast in Central China's Hunan province that killed 20 people on Saturday.

Family members of victims of a deadly tunnel blast wait near the Baimianshan tunnel, Yanling county, Central China's Hunan province, on Sunday. The explosion on Saturday killed 20 people.?[Photo / for China Daily?]

The blast at a highway construction site occurred when explosives were being unloaded from a vehicle.

A spokesman for the State Administration of Work Safety, who requested anonymity, said on Sunday that the vehicle carrying the explosives belonged to the construction team building the tunnel. He also said that safety rules were violated as more than one person was in the vehicle at the time.

"The regulations state that there must not be any passengers in a vehicle transporting explosives."

The victims of the blast were in close proximity to the vehicle.

"More than 200 kilograms of explosives were in the vehicle as the blast happened," the spokesman said.

Preliminary investigations show that the blast occurred at about 8:20 am Saturday in Baimianshan tunnel and that 24 people were in the tunnel at the time.

The tunnel, 2,355 meters long, is being built for an expressway between two counties, Yanling and Rucheng, in the province.

Twenty workers died and four were rescued. Of them, one worker is in serious condition and another slightly injured. Two others escaped injury, according to provincial authorities. The injured are being treated in a nearby hospital. The bodies of 19 workers have yet to be retrieved.

The blast occurred as explosives were being unloaded. The explosives were contained in 12 cases and each weighed about 24 kg.

Wang Biao, head of a rescue team organized by the fire department in Yanling county, in the province's Zhuzhou city, told China Daily that there was little chance of finding any survivors.

"We dispatched 12 fire fighters to the blast site at about 1:50 pm on Saturday and seven of them left the tunnel at midnight on Sunday," Wang said.

Firefighters will remain at the scene on standby, Wang said.

Immediately after the blast there were initial fears that the tunnel might collapse, but despite the danger rescuers went in and managed to pull one man to safety.

The tunnel has been made safe for public use, Wang said.

After the blast, provincial departments, including police, fire, health, transport and work safety administrations, arrived at the tunnel and coordinated search and rescue work and launched investigations, according to provincial authorities.

Relatives of the victims are being comforted by police and officials from various provincial departments, as well as other workers on the project.

An official of the China Railway No 3 Engineering Group, who declined to give his name, said the cause of the explosion is not yet known and investigations are under way.