Two Chinese people suspected of having Sars were confirmed as having had the flu-like disease, but one has recovered and the other was in stable condition, China's health ministry said on Saturday.
The cases - a 20-year-old waitress who worked in an exotic game restaurant and a 35-year-old businessman - bring the total number of confirmed new Sars cases in China to three.
Both cases were in the southern province of Guangdong, where Sars first emerged in late 2002 before spreading to more than 30 countries, infecting about 8,000 people and killing nearly 800.
The waitress was released from hospital on Saturday, and none of the people under medical observation for being in contact with her had shown any signs of Sars.
None of the businessman's associates had shown any Sars-like symptoms, either.
In a statement on its Web site (www.moh.gov.cn), the ministry said health professionals must be on guard to prevent an outbreak during the week-long Lunar New Year holiday when hundreds of millions of people pack trains, buses and airplanes.
"It has not been very infectious and the victims have recovered quickly, but we cannot become careless or relax our vigilance," a ministry spokesman said in the statement.
World Health Organisation experts see civet cats as prime suspects in the spread of Sars after finding traces of the deadly virus in cages in a restaurant where a patient served up civet dishes.
Zhong Nanshan, the head of the Guangzhou Respiratory Disease Research Institute, said the next few weeks would be critical to controlling the disease, but he did not expect an outbreak similar to last year's.
"Of these three people, transmissibility was very weak and the symptoms were very light," Zhong told Hong Kong's Cable Television. "I think the situation will not be like last year, whether in Guangdong or Hong Kong," Zhong said.
The ministry's confirmation comes days after media in Hong Kong, the freewheeling city bordering Guangdong, said the waitress had been confirmed as an actual Sars case.
On Saturday, Hong Kong's Apple Daily cited unidentified sources as saying five mainland reporters were under surveillance after being detained for leaking details of the waitress to non-mainland media.
Chinese authorities recently detained the editor of the Southern Metropolis Daily, which first reported the return of Sars in Guangzhou.
Chinese media have been under strict orders since last year to stick to the daily Sars updates by the Health Ministry, which did not report the case until after the Southern Metropolis published the article.
The five reporters, including at least one from Southern Metropolis Daily, had been released but remained under surveillance, the Apple Daily said.
Officials from the Chinese government or newspaper were not immediately available to comment on the report.