Meanwhile, scientists in Canada announced Sunday that they had identified the genetic code of the virus suspected of causing SARS — a surprisingly rapid achievement that is the first step toward a diagnostic test and possible vaccine.
State television showed Hu visiting hospitals in the hard-hit southern province of Guangdong and four new fatalities from severe acute respiratory syndrome were reported, raising China's death toll to 64. Dozens of new cases also were reported — 47 of them in a single province.
State media quoted Premier Wen Jiabao as saying the situation "remains grave" and warning that China's economy, international image and social stability could suffer. He called for airline and train passengers to be screened and quarantined if necessary.
"Since the discovery of the SARS cases, I feel very worried. I feel anxious for the masses," Hu was shown telling medical workers on state television.
It was his first public comment on SARS and, in an unusual step, the national evening news broadcast his own voice instead of having an announcer read his comments.
In Canada, the hardest hit country outside Asia, scientists at the British Columbia Cancer Agency in Vancouver worked 24 hours a day for six days to sequence the genetic code of the virus suspected of causing SARS.
Researchers reported that the gene sequence suggests a previously unknown coronavirus unrelated to any known human or animal viruses.
Their rapid completion was an "extraordinary step," said Dick Thompson, a spokesman for the World Health Organization in Geneva, which has tracked the spread of SARS.
Global health authorities suspect SARS emerged in China, where the communist government has been accused of failing to release enough information about the outbreak.
The reports Monday suggested that Chinese leaders finally have mobilized. The declarations of concern followed weeks of assurances by state media that the disease was under control.
"Much progress has been made in combating the disease ... but the overall situation remains grave," the Xinhua News Agency and newspapers quoted Wen as saying at a national meeting Sunday on fighting SARS.
Wen demanded "effective and powerful measures to prevent the spread of the virus ... and immediate treatment to ensure people's health," the China Daily newspaper said.
On Monday, the Health Ministry reported three fatalities in Shanxi province and one in the Inner Mongolia region, both in China's north, the World Health Organization announced.
Five Mongolians are hospitalized and one is in quarantine after all visited the same Chinese hospital, a health official there said Monday. All six received medical treatment in Hohhot in northern China's Inner Mongolia region in late March.
Worldwide, the death toll is at least 137.
Also Monday, a health official in Shanghai said seven foreigners hospitalized there in a special ward for foreign SARS cases have been found not to have the disease. Doctors concluded they had colds and some have been released, said Song Guofan, the spokesman of the Shanghai Municipal Health Bureau.
Song wouldn't identify the patients, but the U.S. Consulate in Shanghai said last week that two were Americans. Shanghai has reported one confirmed SARS case, which it says is a Chinese woman.
China has reported more than 1,300 cases of infection, most of them in Guangdong province, which has reported 47 deaths.
The chief executive of the Hong Kong Hospital Authority has recovered from SARS and was discharged Monday after three weeks of treatment, officials said.
William Ho is one of 299 of the 1,190 people sickened in Hong Kong by SARS who have recovered and been discharged.
Hong Kong reported seven new SARS deaths on Monday, for a total of 47.
Singapore reported seven new cases of severe acute respiratory syndrome on Monday, bringing the total in the city-state to 158. Nearly 600 people remain under home quarantine, and almost 30 of Singapore's cases are linked to a single patient at Singapore General Hospital, whom authorities call a "super spreader" of the virus.
Despite Wen's warning about SARS possibly being spread by travelers, China's biggest trade fair is to open as planned on Tuesday in Guangzhou, the Guangdong provincial capital. Local officials have promised to disinfect taxis, buses and other public spaces in an attempt to reassure foreign visitors.
Travel agents and businesses in Guangzhou say thousands of foreign business people have canceled plans to attend the Chinese Export Commodity Fair because of anxiety about SARS. Organizers say the event, also known as the Canton Trade Fair, drew 120,000 visitors last year from more than 150 countries.
Elsewhere, the week-long Shanghai International Auto Exhibition is to open April 21 as scheduled, said Guo Yiqun, a spokesman for the organizers. He said they were having the exhibition halls sprayed with disinfectant, planned to have doctors on hand during the event and would give out surgical masks to visitors.
Other international events in China have been canceled due to disease worries — tournaments for rugby and women's ice hockey and a United Nations meeting on intellectual property.