HONG KONG -- Asian governments are stepping up precautionary measures to prevent an outbreak of a mysterious illness after Chinese health authorities reported 44 cases of a "viral pneumonia of unknown origin" amid concerns that the flu-like virus is linked to the highly contagious SARS virus that caused hundreds of deaths in Asia and elsewhere 17 years ago.

The outbreak prompted authorities in Hong Kong, Macao, Taiwan, South Korea, Singapore and Malaysia to take emergency measures, including stricter health control at borders and temperature screenings on all flights from Wuhan, in China's central Hubei Province, where the outbreak originated. Chinese officials said on Friday that 11 patients remained in critical condition with respiratory tract infection symptoms, including fever and breathing difficulty.

Health authorities in Hong Kong were on high alert following five cases of patients developing symptoms of respiratory infections and fever after visiting Wuhan, about four hours by train from Hong Kong. Two of the patients have been discharged from the hospital following a full recovery and a third has tested negative for SARS, influenza and avian flu. The government said on Friday evening that two others are awaiting test results.

"No serious pneumonia cases linked to the Wuhan outbreak had been reported in Hong Kong so far," Sophia Chan, Hong Kong's Secretary for Food and Health, said late Thursday night.

The Hong Kong government has rolled out new prevention measures, including a daily announcement of any suspected cases, installing additional thermal imaging systems at Hong Kong International Airport, as well as increasing steps to clean and disinfect incoming express trains and planes from Wuhan.

Health workers evacuate "infected patients" from a building during a SARS outbreak drill in Hong Kong in November 2004. Authorities considered it necessary to heighten alertness over infectious diseases. © Reuters

"Investigations are still being carried out and authorities cannot yet confirm what pathogen is causing this illness," a senior adviser with the World Health Organization in China told the South China Morning Post on Wednesday, adding that it has set up an incident management team to "ensure disease detection systems are sensitive, communication channels are open, and reporting is rapid across the region."

Yuen Kwok-yung, a microbiologist at the University of Hong Kong, told local media on Wednesday that the viral infection in Wuhan appeared similar to the 1997 outbreak of bird flu and the SARS epidemic in China. He said there are chances that animals also carried the virus in the latest outbreak.

"At the moment we still haven't identified anything significant," Yuen said, urging the public not to worry.

SARS, or severe acute respiratory syndrome, which emerged in southern China in late 2002, infected over 8,000 people and killed 775 globally. China dismissed its health minister at the time, Zhang Wenkang, after being criticized by the WHO for covering up and underreporting the number of SARS cases.

All patients in the Wuhan outbreak have been held in isolation and their close contacts are under medical observation. Initial lab tests that showed "no apparent human-to-human transmission" and no medical staff were infected, according to the Wuhan Municipal Health Commission. Most of the patients worked in a seafood wholesale market, the commission said in a separate statement.

Local media reported that the market, which has since been shut down, sold other wildlife, such as rabbits, snakes and pheasants. A team of experts from China's National Health Commission are "currently conducting relevant inspection and verification work," state broadcaster CCTV reported.

Hong Kong’s Secretary for Food and Health, Sophia Chan, second from left, on Jan. 2 chairs a meeting to examine prevention measures adopted in response to the pneumonia cases detected in Wuhan. (Photo from Hong Kong’s Information Services Department)

"The cause of the current outbreak is not clear, and it cannot be concluded that it is the SARS virus as rumored online," the state newspaper People's Daily said on microblog Weibo. Wuhan police said it has detained eight people for spreading false news online about the case.

In Taiwan, authorities have ramped up border screening efforts of flights from Wuhan. Health officials are conducting onboard inspections and promoting health awareness before passengers are allowed to disembark, said Chou Jih-haw, director-general of Taiwan's Centers for Disease Control. He said that a six-year-old passenger who developed a mild fever after transferring in Wuhan is now under health monitoring at home.

Health authorities in Macao, which has two daily direct flights from Wuhan, began temperature screenings on all inbound aircraft from the city on New Year's Day. Similar measures are in place in South Korea, said Park Hye-kyung, a senior official at Korea Centers for Disease Control & Prevention, which has launched an emergency center to deal with the issue.

At Singapore's Changi Airport, travelers arriving from Wuhan began undergoing temperature screenings on Friday.

"Suspect cases with fever and acute respiratory illness or pneumonia and with travel history to Wuhan within 14 days before the onset of symptoms will be isolated as a precautionary measure to prevent transmission," Singapore's Ministry of Health said in a statement, adding that no suspected cases had been found so far.

Malaysia's Health Ministry also unveiled measures to examine fever-like symptoms at all international borders.

None of the regional authorities have expanded inspections and screening measures to cover other parts of China.

Additional reporting by CK Tan in Shanghai, Kentaro Iwamoto in Singapore, Kim Jaewon in Seoul, Lauly Li in Taipei, P Prem Kumar in Kuala Lumpur and Skylar Li in Hong Kong.