China has given its strongest indication yet that a man taken into hospital last week may have Sars.
Anti-Sars measures are being stepped up again in Chinese cities
Gene sequencing results showed the patient may be infected with the Severe Acute Respiratory Syndrome virus, the official Xinhua news agency reported.
Confirmation may come from other tests being carried out in Hong Kong.
Sars triggered a worldwide health crisis in 2003 and, if confirmed, this would be China's first case since it contained the outbreak in July.
The latest suspected Sars case is a 32-year-old television producer who is being monitored on closed-circuit television in hospital in Guangdong province, where the respiratory disease first emerged in late 2002.
"There is a possibility that the patient may have contracted the Sars... virus," Xinhua reported, citing results from tests at a Guangdong laboratory.
Testing on samples from the patient is also under way in two laboratories affiliated to the World Health Organisation in Hong Kong, a WHO spokesman said.
"It is clear that the male patient... has suffered from pneumonia and displayed signs and symptoms that could fit the profile of Sars," the WHO said on its web site.
"However, such signs and symptoms could also be caused by a large number of other infectious diseases."
Whatever the outcome, the WHO predicts that China's radically raised level of alert and resources devoted to curbing Sars will prevent major outbreaks, the French news agency AFP reports.
On Tuesday, a Taiwan army medical researcher who contracted Sars in a laboratory was discharged from hospital after doctors decided he could no longer infect other people.
Sars is estimated to have infected more than 8,000 people, of which 774 died.