May 1 (Bloomberg) -- Hong Kong confirmed its first swine flu case today, prompting the government to declare a public health emergency. It is the first confirmed case in Asia.

The unidentified 25-year-old Mexican man flew into the city yesterday from Shanghai on China Eastern Airlines Flight 505 after originally departing from Mexico, Chief Executive Donald Tsang said. The University of Hong Kong confirmed the infection at 8 p.m. today.

“I’d urge Hong Kong citizens to not panic,” Tsang said at a news conference. “School classes, public exhibitions, economic activities can all proceed as usual.

“I want to emphasize that I’d rather take a stricter approach than missing the opportunity to contain the virus before it spreads.”

The man arrived in Hong Kong with two companions after changing planes in Shanghai. They did not leave the airport there, York Chow, the city’s health secretary, said at a later news conference.

After arriving in Hong Kong, they took a taxi to the Metro Park Hotel in the city’s Wanchai district. The man started feeling sick at around 7 p.m. and went to nearby Ruttonjee Hospital, where he was quarantined immediately while tests were conducted, Chow said.

The first test was negative. A second test by the university showed he had the flu. Three other people he came into contact with are quarantined in Princess Margaret Hospital.

Police cordoned off the hotel today, and Chow said people there would be quarantined for a week. One man wearing a surgical mask was seen carrying boxes labeled “Tamiflu” into the hotel lobby.

The patient and his companions were prescribed Tamiflu, Chow said. Hong Kong has 20 million doses of Tamiflu, made by Roche Holding AG, and other anti-flu medicines in stock, the South China Morning Post reported April 27.

Authorities are trying to track down the taxi drivers who drove the infected man to the Metro Park Hotel and to the hospital, and want to check on the passengers who sat near him on the flight from Shanghai to Hong Kong.

“We still do not know how damaging this virus will be,” Chow said.

The city has informed the World Health Organization, China’s Health Ministry and Shanghai health officials.

WHO lifted its six-tier alert to 5 on April 29 and said a move to the next and final level, for the world’s first influenza pandemic since 1968, may soon be made. The virus, known formally as influenza A (H1N1), has reached 11 countries and is confirmed to have infected more than 330 people, according to the WHO’s Web site.

Hundreds more cases are suspected in New York, Mexico, Australia and New Zealand.

Hong Kong is “well-equipped” to handle a swine flu outbreak because of its experience with the deadly severe acute respiratory syndrome, or SARS, in 2003, Tsang said yesterday.

That outbreak killed 299 people in Hong Kong and 774 worldwide. Travel to Asia plunged.

The city will spend HK$10 million ($1.3 million) on extra cleaning of hospitals, public housing estates, schools and offices. Quarantine centers for infected people also are being set up.

To contact the reporter on this story: Hanny Wan in Hong Kong at hwan3@bloomberg.net

Last Updated: May 1, 2009 10:41 EDT