Zhang Chuandong, an official at the heating group, told China Daily that old and corroded pipes were likely to blame for the tragedy.

"The pipes are easily corroded by rainwater and polluted water, and the leaking hot water loosened the earth supporting the pavement," Zhang said.

At the group's pipe repair site on Beilishi Road, the emergency team leader said the cracked pipes had been in use for at least 10 years, but he could not confirm the situation at the accident site as the pipes were four meters underground.

Zhang said on Wednesday 78 meters of pipes had been replaced and repairs would be finished on Thursday.

However, Zhang said the pipe maintenance was actually the responsibility of Wuhua Mansion, an office block near the scene of the accident. After the previous regular examination, his group had asked the building to repair the broken pipes, he said.

An official of the property management department of Wuhua Mansion, who did not wish to be named, said he did not think it was their duty to maintain the pipes.

"The pipes are out of our management area because they are under the road," the official said. He said that steam had been rising from the pavement for a long time, but was ignored.

"We reported it to the heating group after finding hot water leaking from the ground before the accident occurred. Repair workers came to close a valve, but didn't take emergency measures, such as setting up a warning sign," he said.

He claimed that the developers of Wuhua Mansion had paid 320,000 yuan ($50,800) toward the victim's medical treatment, but "which party should finally pay compensation will depend on who is deemed responsible by the investigation team".

A colleague tends to the victim at the scene of the accident.