The swift and vigorous action was an indication that officials are eager to prove they have learned from the deadly spread of SARS in 2003, when they were criticized for imposing quarantine measures too slowly.
With the disease on its doorstep, mainland China suspended all direct flights from Mexico, the virus's epicenter, and was checking and holding in quarantine other travelers on the same flight as the 25-year-old Mexican who became Asia's first confirmed case of the virus late Friday. He landed first in Shanghai before continuing on to Hong Kong.
In Beijing, the vice director of Ditan hospital, Chen Jun, said 15 people from the flight were at the hospital for observation but had not shown any symptoms of influenza. Five were Mexican and the rest Chinese. In addition, one passenger each who went to Jiangsu and Hebei provinces have been placed in quarantine, he said.
China was looking for 15 people in Shanghai and 11 people in southern Guangdong province who were also on the plane.
Officials in Taiwan and Hong Kong were looking for other passengers and others who may have come into contact with the man, including his taxi drivers. Hong Kong Secretary for Food and Health York Chow said the government has already tracked down 19 people who sat near the Mexican on the plane and isolated them.
South Korea, meanwhile, reported the continent's second confirmed case in a woman who has been under quarantine since earlier this week when she returned from Mexico.
Sixteen people in the Latin American country and one toddler in the U.S. are confirmed to have died from the disease. More than 650 cases have been confirmed worldwide, with 397 in Mexico. Canada, Israel, New Zealand and more than a half-dozen European countries also have confirmed cases.
Though U.S. officials have already begun to express hope the epidemic may fizzle, authorities took no chances in Hong Kong. Experts fear the disease will be more difficult to contain if it begins to spread through Asia's densely populated countries.
Health workers in white bodysuits patrolled the lobby of the Metropark Hotel in Hong Kong on Saturday as guests picked up bottles of water, chocolate milk and bread before returning to their rooms by elevator. About a dozen police officers wearing masks guarded the building, which was cordoned off.
Chow said the territory was facing "a critical moment."
An Australian tourist who spent the night with friends in a Hong Kong suburb returned to the hotel Saturday morning to join the quarantine.
James Parer, 38, told reporters as he entered the building that he was not worried because the territory could draw on experience from its battle with SARS, or severe acute respiratory disease.
"Hong Kong is the best place this could happen because it should be best prepared," said Parer, who was visiting Hong Kong from Brisbane to attend a trade fair.
During the SARS outbreak, an infected doctor who checked into a Hong Kong hotel later died, but not before infecting a resident of the Chinese territory and 16 other hotel guests. Those guests spread the virus internationally, and it eventually killed more than 770 people, including 299 in Hong Kong.
But a Hong Kong infectious diseases specialist criticized the quarantine as a political move that served little purpose because it only locked down a small group of people and scared away tourists.
"This is only one point in his journey. And it's not the highest risk point in his journey. Flu spreads through coughs or sneezes at close range. People who lived above and below him are nearly not at risk at all," Lo Wing-lok said.
Hong Kong leader Donald Tsang defended his decision, saying: "I'd rather err on the side of caution than miss the opportunity to contain the disease."
A World Health Organization spokesman stopped short of a wholesale endorsement of the move but indicated the U.N. agency was pleased.
"We don't have a policy on quarantining hotels in situations like this, but we like governments to be as sure as they can that they're controlling the situation rather than missing opportunities. So in that context, we're happy with what Hong Kong has done," Peter Cordingley said.
Another Hong Kong infectious diseases expert, John Simon, echoed others who said the territory was a special case. "We're more unique than most cities in the world because of our population density," he said.
Reporters swarmed around the Metropark, in the city's Wan Chai bar and office district, pressing pieces of paper with their phone numbers against the lobby's window. Photos that ran in Hong Kong newspapers Saturday showed one masked guest flashing a handwritten sign to journalists that said, "We will exchange information for beer and food and cigarettes."
Officials have conducted medical checkups on about 200 of the guests and staff holed up at the Metropark. Sixty people who had mild symptoms were taken to hospitals for follow-ups, Thomas Tsang, controller of Hong Kong's Center of Health Protection, was quoted as saying on radio RTHK's Web site Saturday.
Twelve guests who didn't want to stay at the hotel were moved to a suburban holiday camp. The quarantine will last seven days at both locations.
Kevin Ireland, a Metropark guest visiting from India on a business trip, said some guests appeared anxious and others were just bored.
"I'm not worried, but there are some people who are really panicked," Ireland, 45, told The Associated Press by phone from within the hotel. "We don't have any books to read. It's boring, but what can one do?"
The Mexican patient, who was not identified, arrived in Shanghai on AeroMexico flight AM 98 and continued on to Hong Kong on China Eastern Airlines flight MU 505. He developed a fever after arriving in the territory Thursday afternoon and is now in stable condition and isolated at a hospital.
In New Zealand, the first country in the Asia-Pacific region with confirmed cases, the tally remained at four Saturday, Health Minister Tony Ryall told reporters.
2009 H1N1 Flu Outbreak Map:
This is a map depicting confirmed and suspected cases of the 2009 H1N1 outbreak, with contributors from all over the world, from a variety of backgrounds including health, journalism, technology.
By Associated Press Writers Dikky Sinn and Min Lee