The chances of finding survivors in the rubble after a devastating earthquake in China are fading fast, a rescue expert said, as his British group struggled to gain permission to enter the country.

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

Looking for miracles

"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 to help find survivors in areas destroyed by Monday's quake.

By 2pm on Thursday, it was 72 hours since the 7.9-magnitude earthquake struck, leaving more than 40 000 dead or missing in southwestern Sichuan province, many buried under collapsed buildings or landslides.

But despite the tragedy, China has been slow to let rescue teams enter its territory, and McMartin said unless they get permission later on Thursday or early Friday, they will be unable to provide much assistance.

"We have had problems getting into other countries before, but generally it is not as bad," said McMartin, whose team have helped rescue efforts following many major disasters, including quakes in Turkey, Pakistan and El Salvador.

He added that if the charity had not been given permission to enter by Saturday, it would be forced to drop its plans.

"That would be a travesty... We have not come here to dig up bodies, we have come here to rescue people," he said.

McMartin's volunteer team, which includes firefighters, medical professionals and engineers, tried to confirm permission before leaving the UK, but were told they would only be able to apply when they arrived in Hong Kong.

China has been reluctant to allow foreign teams to enter its territory, and only gave permission for a Japanese rescue group to provide assistance on Thursday.

Teams from Hong Kong and Taiwan, which China considers part of its country, have also been allowed to enter.

A race against time

However, both Australia and South Korea earlier said Beijing had declined offers of help, despite the race against time to rescue survivors trapped under rubble in towns scattered across the remote and mountainous disaster zone.

China has recently stepped up its border controls ahead of the Olympic Games, making it more difficult for both tourists and business travellers to enter the country, travel agents have said.

One girl was pulled from the rubble 50 hours after her school was destroyed, state media said.

AFP