'The deaths are estimated to be over 50,000,' state television said, quoting the latest figures from the national quake relief headquarters, adding that the confirmed toll had reached 19,509.

Time is running out
The chances of rescuing survivors trapped by rubble and landslides will drop after Thursday, a rescue expert said in Hong Kong.

'Most people are saved in the first three or four days,' said Mr Willie McMartin, director of British-based charity International Rescue Corps, which has helped save people's lives in disasters across the world.

'People can survive up to 15 days, but that is when you are talking about miracles and miracles do not happen very often.

'We would normally slow down our rescue operations a week after the earthquake happened,' he told AFP in Hong Kong, where his 10-strong team are trying to secure permission to enter China.

Widespread damage
The full scale of the devastation is only now beginning to emerge as teams hike into the remote epicentre of Monday's powerful 7.9-magnitude earthquake.

In Yingxiu, a town of about 10,000 people where the epicentre of the quake struck, most of the buildings had collapsed and a desperate relief effort was underway for the survivors, an AFP reporter witnessed on Thursday.

'I want to go home. I miss my mum and dad,' said a 21-year-old girl from a nearby town who was visiting her boyfriend here when the quake hit.

Public appeal and road repairs
The government issued a rare appeal to the Chinese public calling for donations of rescue equipment including hammers, shovels, demolition tools and rubber boats. The plea on the Ministry of Information Industry's website said, for example, that 100 cranes were needed.

Roads were cleared to two key areas that felt the brunt of the quake?s force, with workers making it to the border of Wenchuan county at the epicentre and also through to hard-hit Beichuan county, Xinhua reported. Communication cables were also reconnected to Wenchuan.

New threat; Dams bursting
The country's water minister warns of widespread damage to dams.

Chinese state media have said troops rushed to repair cracks in the Zipingpu Dam in Sichuan province caused by the earthquake on Monday.

But Minister for Water Resources, Chen Lei, said such damage was widespread and sounded far from assured in comments put on the ministry website on Thursday.

'Especially in Sichuan province, there are many dams, damage from the quake is extensive and the hazards are unclear,' Mr Chen said in the speech given to officials a day earlier.

'Blockage of waterways can be extremely sudden, and draining them is difficult.'

And the minister blamed more than nature for the dangers.

'Because the management systems of hydro-power stations are not smooth and information channels are blocked, the extent of their damage is unclear,' Mr Chen said.

The mountainous western half of Sichuan has been a magnet for hydro-power projects, hoping to profit from China's huge thirst for energy.

As China struggles to cope with about 15,000 dead and many more people missing or displaced from the quake, the vulnerable dams in the region are another threat. One dam burst could unleash a cascade of uncontrolled water, threatening other dams and residential areas.

The ministry said earlier that additional water has been released from the damaged Zipingpu reservoir, which could 'bring disaster' to the city of Dujiangyan downstream if it burst. Mr Chen ordered officials to plan for evacuation of endangered people if dams threaten to burst.

Large scale airdrops
China's state-run Xinhua news agency said large-scale airdrops would begin later on Thursday, flying more than 50,000 food packets and tens of thousands of items of clothing and blankets into the areas worst hit.

The military is also deploying 30 more transport aircraft to ferry rescuers and supplies across Sichuan province, and a reporter saw dozens of army trucks heading north to the disaster zone from the provincial capital Chengdu.

Helicopters are especially vital to the relief effort as much of the quake area consists of mountain villages and towns cut off by huge landslides. - AFP

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