The WHO experts will help Chinese experts double-check test results on the hospitalized man and track down anyone else who might have had contact with him, said Dr. Julie Hall, the SARS team leader for WHO's Beijing office.
The patient, a 32-year-old television producer, is hospitalized in Guangdong province, where severe acute respiratory syndrome first emerged in 2002.
China's prompt announcement Saturday of the suspected case — its first since July — and its collaboration with WHO are in contrast to the earlier outbreak, when Beijing was criticized for its sluggish response and failure to respond to pleas for information and cooperation.
China has given information "very freely" to an Australian laboratory expert also sent by WHO, Hall said.
"From what we've seen and all the information that has been shared with us, the correct steps have been taken" to isolate the patient and track down people who had contact with him, Hall told The Associated Press.
Chinese experts have found only "inconclusive results" from repeated tests on samples from the man, Hall said.
"This case at the moment has clinical symptoms that would fit SARS but at the same time his pneumonia could be explained by many other different disorders," Hall said.
"It is important that we get the correct result, so many tests will have to be repeated," she said. "And there is a possibility that samples may have to leave China and go to an international reference laboratory."
SARS killed 774 people worldwide and sickened nearly 8,100 before subsiding in June.
The flu-like illness claimed 349 lives on China's mainland and more than 5,000 were sickened. Beijing declared the mainland's last 12 patients free of the disease in July.
The WHO experts will try to help figure out where the man in Guangdong might have contracted the virus, Hall said. She said he didn't have any known contact with high-risk groups such as health workers or animal handlers before becoming sick.
Meanwhile, people quarantined after having contact with the new suspected case are expected to finish medical observation within a week, the state newspaper China Daily said. It said 32 of those people are medical workers.
The discovery prompted China to step up screening for possible cases of severe acute respiratory syndrome, ordering train stations and airports to check travelers for fever.
"The whole (Chinese anti-SARS) system is a lot stronger than it was at the beginning of the year," Hall said.
The suspected case was hospitalized Dec. 20 with a headache and fever, according to the government. He was transferred last Wednesday to a quarantine ward and declared a suspected SARS case on Friday.
On Sunday, the man was in stable condition and his temperature was normal for the fourth straight day, according to China's Health Ministry.