China confirmed a possible third SARS case yesterday, a 35-year-old man isolated in hospital after showing symptoms of the respiratory disease, and the World Health Organisation sought clarification on a possible fourth.

The man was labelled a suspected case yesterday, Xinhua news agency quoted a health official in the southern province of Guangdong as saying. He had earlier been under observation as a possible case.

Last week, China confirmed its first case of Severe Acute Respiratory Syndrome since a world outbreak was declared over in July. He has since recovered.

A waitress is also in hospital suspected of having the deadly flu-like disease, which experts suspect has jumped from animals to humans. All three patients were in the Guangdong capital, Guangzhou, when they fell ill.

The 35-year-old man was described by a local official as a ?self-employed investor? and Xinhua said he had apparently had no contact with SARS patients or animals that might carry the virus. He was taken to the No. 8 People?s Hospital, one of three hospitals in Guangzhou designated for SARS treatment.

Experts distinguish between a person being observed for SARS symptoms and a suspected case. Designation as a suspected case depends on observation, various tests, which could take several days, and consultation between local medical authorities and the Health Ministry, the World Health Organisation (WHO) said.

The WHO also said it was asking the Health Ministry and local authorities about rumours of a possible fourth SARS case under observation in the boomtown of Shenzhen, near Hong Kong.

?We will look for more clarification,? spokesman Bob Dietz said.

A spokeswoman for Shenzhen?s health department said he had not heard of a possible fourth case. ?We do not know of any SARS-related case in Shenzhen,? she said.

China confirmed its first case of SARS, a 32-year-old television producer named Luo, on Monday last week.