The French experts of the Institute for Radiological Protection and Nuclear Safety (IRSN) said several nuclear installations not used for electricity generation were located in the south-western province at the epicentre of the quake.

These included a manufacturing site for nuclear weapons which handles unstable chemical elements found in tritium, plutonium and uranium, as well as a nuclear reactor.

The IRSN said that given the effects of Monday's 7.9-magnitude quake, "it is not possible at this stage to exclude damage to these installations."

However, no radioactive leaks had yet been found, the Paris-based monitoring organisation said, citing memos from China's National Nuclear Safety Administration (NNSA).

The IRSN said the Chinese nuclear safety watchdog had launched its crisis action programme, but that environmental test results had given it the all-clear.

"All relevant NNSA installations within Sichuan province were immediately put on security alert," said an IRSN statement.

Older nuclear installations undergoing de-commissioning were found to have suffered slight damage owing to less stringent anti-seismic or earthquake construction regulations in past eras.

But current buildings and equipment were found to be unscathed, the NNSA stressed.

The scale of the quake -- which rattled buildings across China and in cities as far away as Thailand and Vietnam -- has become clearer after rescue teams hiked to remote towns cut off by landslides.

The confirmed death toll stood late Friday at 22,069, state media said, with officials in Sichuan saying another 14,000 remained buried.

But state television, quoting figures from national quake relief headquarters, said the government estimates the death toll at more than 50,000.

Another 4.8 million people have been left homeless by the disaster, officials in Sichuan added.

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