The death toll in China’s deadliest tremor in 32 years could soar to 50,000, state media reported yesterday, as time was running out to find survivors trapped in the rubble.

Soldiers and rescue teams from across the country were picking through the rubble of schools, homes and factories but mechanical diggers were already rumbling across ruins where survival was deemed impossible.

The grim search for bodies sometimes brought a surprise. In Yingxiu, a town at the epicentre, rescue workers pulled an 11-year-old girl out of the rubble 68 hours after her school crumbled. Rescuers were sifting through the debris when they heard a voice. "It's wonderful, she's alive!" a delighted onlooker shouted as the girl was pulled out on a stretcher and given a small cup of water.

Officials raised the death toll to 19,509 and state media said the final figure could be as high as 50,000. More than 12,000 were still buried and 102,000 were injured in Sichuan province at the heart of the tremor.

Experts said the opportunity for rescues was narrowing. Gu Linsheng, a researcher with Tsinghua University's Emergency Management Research Centre, said: “Anyone buried in an earthquake can survive without water and food for three days. After that, it's usually a miracle for anyone to survive.”

The government has already deployed 130,000 troops and added 90 helicopters to the operation. Military convoys and columns of ambulances filled the roads while helicopters buzzed overhead. But the authorities were short of equipment, appealing for trucks, 100 cranes and even hammers, shovels, demolition tools and rubber boats.

With more and more bodies being uncovered and with many more still waiting to be found, health officials warned of the need to be on alert against disease. Vice Health Minister Gao Qiang said: “This is only a beginning of this battle, and a long way lies ahead of us. For every thread of hope, our efforts will increase 100-fold. We will never give up.”

Tales of tragedy far exceeded moments of hope. Gu Qinghui of the International Federation of Red Cross and Red Crescent Societies visited the devastated town of Beichuan that was first flattened by the tremor and then buried by landslides. He said more than four million homes were shattered across the quake area. “The whole county has been destroyed. Basically there is no Beichuan county any more.”

Weakened dams continue to pose a threat. Chen Lei, the Minister for Water Resources, said damage was widespread. “Because the management systems of hydro-power stations are not smooth and information channels are blocked, the extent of their damage is unclear."

As many as 920 dams of all sizes had suffered damage in the earthquake, The Times has learnt. One expert said few were in any danger of collapse, although officials were making extra checks at one near the town of Wudu not far from the epicentre.

An official from Huaneng Power Group said contact had finally been established with 110 people trapped at a hydropower plant near the devastated town of Yingxiu. “The big problem is the dam faces a danger of collapsing and the water level has kept rising,” he said.

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