The doctor estimated the outbreak in the Chinese capital might be five times greater than officially admitted.
An American teacher who became ill with SARS was driven Wednesday across China's border to Hong Kong, where he was pronounced dead in a hospital, officials said.
Hong Kong had earlier reported two more deaths, bringing the number of fatalities here to 27, and 42 new cases, for a total of 970.
Elsewhere, Malaysia stopped issuing entry visas to most Chinese travelers. Indonesia told its citizens to stop spitting in public places. Singapore's Roman Catholic Church reportedly ordered its priests stop hearing confessions.
Betting that his government can overcome the threat, Thailand's leader promised to pay 2 million baht ($48,000) to families of anyone who dies from SARS and can prove it was contracted during next week's traditional New Year celebrations in the country.
"We're confident there's no SARS," Prime Minister Thaksin Shinawatra said as he doubled an earlier offer of 1 million baht ($24,000) for any death.
In Hong Kong, officials cautiously prepared to let more than 200 people go home from quarantine camps after they showed no signs of SARS.
The American teacher, James Salisbury, 51, had been ill for about a month but he thought he had a minor flu and only sought treatment nine days ago, said his friend, David Westbrook. A hospital spokesman said Salisbury's six-year-old son, Mickey, was taken to another hospital.
SARS has infected more than 2,600 people worldwide and killed at least 106, most of them in mainland China and Hong Kong, with other deaths in Canada, Singapore, Vietnam, Thailand and Malaysia.
A prominent Chinese surgeon accused his government on Wednesday of concealing the full extent of SARS, saying Beijing has several more deaths and five times as many cases of infection as publicly reported.
Doctors and administrators reached by telephone at the hospitals cited by Dr. Jiang Yanyong refused to comment on his claim. Jiang said he had not been contacted by mainland authorities, who typically do not tolerate public criticism, but added, "I don't know what will happen later."
A spokesman for Malaysia's embassy in Beijing said it has been ordered to stop issuing visas to most mainland Chinese until SARS is contained. But members of government delegations and those on business trips can still apply if they are declared free of SARS symptoms such as fever, coughing and breathing difficulties, he said.
Officials have also revoked visa-free travel for citizens of Hong Kong.
The Philippines issued an advisory against unnecessary travel to Hong Kong and the southern Chinese province of Guangdong, citing the SARS outbreak.
More than 150,000 Filipinos work in Hong Kong.
The decisions by Malaysia and the Philippines spell more trouble for an Asian-Pacific travel industry that has been battered by SARS, which has been spread by airplane travelers after apparently originating in Guangdong.
Australian flag carrier Qantas announced Wednesday it will lay off 1,000 staff before the end of June, blaming a drop in traffic brought about by SARS as well as the war in Iraq. Hong Kong's airport has seen hundreds of flights canceled since the World Health Organization warned people not to travel to the former British colony if they could avoid it.