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 that handle 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.