Chinese doctors have been asked to test all survivors of last week's earthquake for a potentially deadly bacterial infection after they had to perform 30 amputations.

Central authorities have told local medical workers to test patients immediately for gas gangrene.

If they test positive, the patients will receive medication and will be isolated to prevent infections from spreading.

The condition consists of a gas infection entering a body part suffering gangrene, a decay of body tissues caused by severe injury.

Gas gangrene can cause death within hours.

Doctors, as of Sunday, found 58 cases of gas gangrene and needed to amputate in 30 cases.

The health ministry is sending some 3,500 epidemic specialists into the earthquake zones and distributing 5.3m leaflets on hygiene tips.

Authorities have said that preventing disease outbreaks among the 5m homeless is a chief concern as hopes of finding survivors from last week's 7.9 Richter-scale earthquake fades.

More than 40,000 people are confirmed dead after the earthquake hit Sichuan province last Monday. Tens of thousands of others are missing, according to the government.