Hong Kong health officials said 60 more people had fallen ill with a deadly flu-like disease, more than half of them in one apartment complex, pushing the number of infections worldwide past 1,600.
Singapore's health minister, Lim Hng Kiang, said the disease may spread more easily than first believed, with some people found to be more infectious than others. Labeled as "super infectors," they can infect as many as 40 others, he said.
"We run the risk of a huge new cluster of infected people, which could start a chain reaction," Lim told a news conference.
The World Health Organization said severe acute respiratory syndrome, or SARS, has killed at least 54 people worldwide, with the majority of cases in Hong Kong and China. That figure does not include three more deaths reported Sunday, one each in Hong Kong, Toronto and Singapore.
The International Ice Hockey Federation canceled the women's world championships scheduled to begin Thursday in Beijing.
Authorities have declared a health emergency in Toronto, located 50 miles from the U.S. border. U.S. health officials have reported 62 cases in the United States.
So far, four people have died from the illness in Toronto, the latest was reported Sunday. In addition, about 100 probable or suspect cases have been reported. Officials have closed two hospitals to new patients, and hundreds of people have been quarantined in their homes.
Another possible case turned up in New Brunswick on Canada's east coast, officials said Sunday, meaning the illness that originated in Asia may now reach across Canada. The New Brunswick case involves a school principal who recently traveled to China.
Other suspected cases are in Ottawa; Winnipeg, Manitoba; and on the west coast in Vancouver, British Columbia.
The United States and Canada have advised people to avoid travel to afflicted areas in Asia, and the World Health Organization recommended that international travelers from Toronto and several Asian cities get screened for symptoms.
Airports are also taking extra precautions, and passengers are increasingly worried, reports CBS News Gretchen Carlson.
"I am staying away from large crowds if possible. But on the plane it's going to be impossible to do that, " said passenger Michael Dean McGar.
Health officials say just one airline passenger infected with the disease could contaminate people two rows ahead and two rows behind.
Singapore said it would station nurses at its airport to examine all travelers arriving from infected areas, while Canada planned to screen those traveling abroad from Toronto, although no system was in place Sunday.
Most of the Toronto-area cases are health care workers at Scarborough Grace Hospital and York Central Hospital who became infected while treating initial victims, all of whom had traveled in Asia or had close contact with other victims.
The disease has caused a run on surgical masks in the city and slowed business by as much as 70 percent at Pacific Mall, a Chinese shopping mall in Toronto's northern suburbs.
Kevin Wong, a worker at a video store in the mall, said the public reaction seemed excessive, but was understandable. Some merchants also were taking precautions, wearing protective masks even though no cases have been linked to the mall.
"People are still coming to work but they're coming in later and leaving early," he said. "They don't want to waste their time when there's no one here."
U.S. health officials said Saturday that none of the antiviral drugs and other treatment they have tested are effective against SARS.
In Hong Kong where 13 people have died, Christians and Taoists held special services Sunday to pray for an end to the epidemic.
Most of the new cases reported Sunday came from Hong Kong's Amoy Gardens apartment complex, where a victim recently spread the disease, according to a Health Department statement.
Some frightened residents have moved out and medical teams have gone through the apartments to check for SARS - while some minibus drivers won't even stop there anymore.
In canceling the women's hockey world championships, the international federation said the spread of the illness to Beijing from southern China put the players at risk.
Players for Canada, the defending champion, were disappointed but understood.
"You could lose your life going there and just being in contact with somebody," forward Danielle Goyette said. "Life is more important than hockey right now."
According to the U.S. Centers for Disease Control and Prevention, people who have become sick since Feb. 1 may have SARS if they suffer from all three of the following: