Rescuers tell of the challenges faced

For a time on Sunday, noisy machinery operating at a gold mine rescue site in Shandong province fell silent.

After drilling a hole to a depth of more than 500 meters, workers paused to listen for any sounds coming from below ground.

The Hushan gold mine in the city of Qixia was rocked by an explosion on Jan 10 that left 22 workers trapped below the surface and damaged a communications system. As a result, rescuers were initially unable to establish whether the miners were still alive.

On Sunday, a rescuer twice banged on a drilling rod lowered down the hole. Team members then listened in vain for any sound being made under the ground.

Two minutes later, the worker banged on the rod twice again, but still there was no response.

Du Bingjian, a chief engineer at the National Mine Emergency Rescue Center, said: "After we tried this several times without hearing anything, I started to become really worried. Had something bad happened to the trapped workers, or were they too weak to respond? They could also have been some distance from the drilling rod or unable to reach it."

He told the rescue worker to bang on the rod five times. This finally produced clear sounds from down below. Rescuers banged on the rod another five times and received the same number of responses.

For further confirmation, workers banged on the rod 27 times in three rounds of nine, receiving a response on each occasion before Du noticed that the sounds coming from below ground were getting weaker.

"We had two experienced doctors listening with stethoscopes to the sounds, but everyone standing around the hole could hear them," said Du, who has worked with emergency teams in mine shafts and helped save more than 300 trapped workers.