China's leaders expressed grave concerns over the deadly SARS outbreak for the first time Monday, following weeks of assurances that the flu-like disease was under control.
In China and Hong Kong, another 11 deaths were reported in the global outbreak that has killed more than 140 people.
Chinese President Hu Jintao was shown visiting hospitals in the southern province of Guangdong, the hard-hit region where severe acute respiratory syndrome, or SARS, is believed to have originated.
"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.
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, among the toughest measures suggested so far as China battles the disease which has killed 64 in the country and sickened more than 1,300.
Four of those deaths were reported Monday, three in Shanxi province and one in the Inner Mongolia region, the World Health Organization announced.
Worldwide, there are more than 3,100 suspected cases of the disease and 144 deaths, mostly in Asia.
In Canada, health officials Monday reported a new cluster of 31 possible cases involving members of a religious community who attended the April 1 funeral of a SARS victim. The 31 people -- 29 member of the religious group and two others who came in contact with them -- were ordered quarantined for 10 days.
Meanwhile, progress was reported on another front: Scientists in Canada and the United States have identified the genetic code of the virus suspected of causing SARS -- a first step toward a better diagnostic test and possible vaccine.
On Monday, Hong Kong reported seven new SARS deaths, for a total of 47. Many of the fatalities have been elderly people or patients suffering from other chronic health problems, although the deaths of six people ages 35 to 52 with no prior health problems were reported over the weekend.
It was unclear whether the mortality rate of SARS was rising or whether there have been more deaths because of an increase in the number of patients, said Dr. Ko Wing-man, acting chief executive of the Hospital Authority.
In Mongolia, five people are hospitalized with what doctors fear may be SARS and one is in quarantine after all visited the same hospital in northern China for treatment, said D. Bat-Ochir, director of the National Center for Infectious Diseases. Mongolia has not reported any deaths or confirmed cases.
Monday's Chinese press reports suggested leaders have mobilized after weeks of complaints about the government's slow response.
"Much progress has been made in combating the disease ... but the overall situation remains grave," the Xinhua News Agency and newspapers quoted Wen, the premier, as saying at a national meeting Sunday on fighting the disease.
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.
Despite Wen's warning about SARS possibly being spread by travelers, China's biggest trade fair was opening as planned on Tuesday in Guangzhou, the Guangdong provincial capital.
Local officials have promised to disinfect taxis, buses and other public spaces, although thousands of foreign businesses have canceled plans to attend the Chinese Export Commodity Fair.