BANGKOK, April 28 -- The World Health Organization said today that the SARS outbreak has peaked and is on the decline in Canada, Hong Kong and Singapore, but not in China, where WHO officials called for detailed disclosure on the progress of the sometimes-fatal respiratory ailment.

"We believe that these countries will still have to make great efforts to control the outbreaks and contain them, but that they're well on the way to decreasing that epidemic curve, so that they will go down to no cases," said David L. Heymann, WHO chief of communicable diseases. "We have great hopes that they will do that, and that they will be free of SARS."

But he said China must work hard to identify cases and control the outbreak of SARS in the provinces.

The U.N. health organization also reported that Vietnam is the first country to successfully contain the virus and will be removed from the organization's list of SARS-affected countries.

Leaders from a number of Asian countries, including Chinese Premier Wen Jiabao, on his first foreign trip, and Hong Kong chief executive Tung Chee-hwa, were to hold a one-day summit here on Tuesday where they were expected to endorse measures to reduce the spread of the disease.

At least 3,106 cases of SARS with 139 fatalities have been reported in China, where the virus was first detected in November in the southern province of Guangdong. The disease then spread to Hong Kong, which has reported at least 1,557 cases and 138 fatalities. Together, the incidence in mainland China and Hong Kong accounts for more than 85 percent of all cases listed by WHO.

The WHO announcement on the decline of the disease in some locations is an indication that the virus, which has killed 321 people worldwide and infected more than 5,000, can be eradicated, officials said.

Since April 11, the number of new infections in Canada, Hong Kong, Singapore and Vietnam has decreased, said Heymann, speaking to a meeting of the Foreign Correspondents Club of Thailand. But China reported 203 new cases of SARS and eight more deaths today.

[Singapore officials on Tuesday said it was too early to say whether the outbreak had peaked in Singapore, as hospitals turned away visitors in an effort to curb the spread of SARS, the Reuters news service reported.

Singapore, coping with the world's fourth-highest number of SARS cases, has gone two consecutive days without a new case, raising hope that tough government measures had made substantial progress in containing the illness.

"We'll have to wait for at least another two weeks," Eunice Teo, a Health Ministry spokeswoman, told Reuters.]

Henk Bekedam, head of the WHO office in Beijing, called on Chinese officials to provide more details about SARS, including detailed identification of outbreaks and the location of patients.

Earlier this month, the Chinese government officially listed only 37 cases and four deaths from SARS in Beijing. Officials later acknowledged mistakes in handling the outbreak and apologized for underreporting statistics about the epidemic. Today, 96 new cases were reported in Beijing, increasing the total there to 1,199, with 59 deaths.

Bekedam said researchers needed to track each new case. "The key question is, what do we know about the 96, who are the 96, when did they start, where did they live?" he said. "This kind of data at this moment is the big challenge."

"We do think that it is now high time that this information becomes available," Bekedam said. "This information is also crucial for everybody to have an understanding from what's going on, and I think at this very moment, we don't know."

Tuesday's summit in Bangkok is an indication of the high level of importance given to fighting the illness, WHO officials said. The Asian leaders were expected to endorse and perhaps expand on standardized detection and protection measures agreed on last week by their health ministers at a meeting in Malaysia. The measures include strict regionwide pre-departure screening of travelers for SARS symptoms.

"To have the head of China and the chief executive of Hong Kong to come to a meeting on SARS is quite a government commitment to confronting the disease," Heymann said. "It never happened with AIDS."

Heymann said the key factor in eradicating SARS appeared to be early detection and an aggressive response. Vietnam has now gone 20 days without a new infection, twice the assumed 10-day incubation period for the disease. Vietnam listed 63 infections and five deaths.

The outbreak occurred in a private hospital, infected mainly health workers, and was rapidly contained, though not through quarantines, said the WHO representative in Vietnam, Pascale Brudon, in a telephone interview from Hanoi. The disease was brought to Vietnam by a Chinese American businessman who arrived from Hong Kong in late February.

"From the beginning, we contacted our network around the world and we were able to inform the government quickly" about the case, Brudon said. An international team was formed and strong infection control measures were established to make sure the infection did not spread beyond health workers, she said. All infections in Vietnam trace back to the one imported case, she said.

WHO said it was dropping travel advisories and was no longer listing Vietnam as a SARS-affected country. But no decision has been made on dropping travel advisories to Toronto, Hong Kong, Beijing and Guangdong province.

Heymann, noting the "unnecessary negative impact" SARS has had on tourism and trade, said that SARS should not prevent people from traveling. He said that there has been evidence of only five confirmed instances of SARS transmission on aircraft, although millions of people have flown since the outbreak was first detected.

"Unfortunately," Heymann said, "the public perceive the risk to be much greater than the risk actually is. SARS is not transmitted to people walking on the main street in any city or town."

SARS is spread by close personal contact with an infected person, he said. The virus is spread by droplets -- through a sneeze or a cough -- or by touching a surface contaminated by the droplets. Evidence further suggests that the contact must take place during a certain early stage of the infection, said Mark Salter, WHO's Geneva coordinator for clinical management of SARS, who also spoke to reporters.Correspondent John Pomfret in Beijing contributed to this report.