Global health authorities were on the alert on Sunday for a severe type of pneumonia that has killed at least nine people, infected more than 100 and sparked a warning from the World Health Organization . The spread of the disease has alarmed travelers. In Hong Kong's international airport on Sunday, many people arriving from Taiwan, Singapore and elsewhere were wearing surgical masks.

"There's nothing we can do about it, so we have to take precautions," one visitor told Hong Kong's Cable TV.

Major carrier Cathay Pacific said on Sunday it had ordered its staff not to check in passengers showing symptoms of the disease and to refer them for medical assessment.

A spokesman for the Geneva-based WHO said there were reports two people had died in Canada, taking the death toll to nine worldwide since the first outbreak of Severe Acute Respiratory Syndrome (SARS), an atypical pneumonia whose cause is not yet known, was detected in China in February.

"This syndrome, SARS, is now a worldwide health threat," WHO director-general Gro Harlem Brundtland said in a statement.

The illness, which starts with flu-like symptoms such as coughing, high fever and shortness of breath, can deteriorate rapidly into pneumonia.

It has infected dozens of people in Hong Kong and Vietnam, many of them hospital staff, and infection numbers have been rising steadily in Singapore and Taiwan.

U.S. health officials said on Saturday they were probing reports that two people passing through Atlanta and New York had the illness. They gave no other details.

Six more infections were reported in Hong Kong and Singapore on Sunday. WHO said it had also received reports of cases in Indonesia and Thailand but it gave no details.

In southern China, 305 people contracted severe pneumonia in February and five died. WHO and other experts are studying if there are links between these cases and others elsewhere.

EMERGENCY TRAVEL ADVISORY

Cathay said one of its passengers had respiratory problems during a flight from Hong Kong to Vancouver on March 6. It was checking if any of its staff had come into contact with the man.

In a rare emergency travel advisory, WHO said a Singapore doctor who treated some of the first pneumonia patients in the island republic had been taken ill and had to be removed from a plane in Frankfurt. He is now in an isolation unit in Germany and 155 other passengers were placed in quarantine.

In Hong Kong, the government has repeatedly played down fears of the virus spreading outside the medical community.

But the Apple Daily newspaper said two women who had likely contracted pneumonia while visiting China's Hangzhou city were rushed to hospital after returning to Hong Kong on Saturday.

A family of six recently in the southern Chinese city of Zhuhai also developed flu-like symptoms after returning to Hong Kong. One of them was now showing signs of pneumonia, it said.

The Hong Kong government has refused to comment on the report. It said there were no signs of any unusual rise in the number of pneumonia cases. There are about 300 cases a week.

Two more hospital staff were hospitalized on Sunday, bringing to 49 the number of cases in Hong Kong, with 42 of them battling severe pneumonia, up from 37 on Saturday.

Health Minister Yeoh Eng-kiong said two patients who had been seriously ill were recovering and one of them would be discharged soon.

"We have effective treatment, but it's not 100 percent," Yeoh said, adding that some patients have responded well to a combination of anti-viral drugs and steroids.

EXPERTS SENT TO VIETNAM

An American businessman died in Hong Kong on Thursday after being flown from Hanoi with respiratory problems.

Four more people in Singapore showed symptoms of the illness on Sunday, bringing the total to 20. Three of them were recently in Hong Kong and the rest are either family, close friends or medical staff who had been taking care of the three.

In Taiwan, three people are battling the illness, with two of them having visited southern China recently.

Singapore and Taiwan have issued travel warnings, a move that will hurt Hong Kong economically. Its tourism industry is one of a few bright spots during the economic downturn.

France and Japan have sent medical experts to Vietnam, where 43 hospital staff are battling the illness in Hanoi. A Hanoi nurse died of the virus on Saturday.

The SARS outbreak follows a bird-flu virus, H5N1, that killed a Hong Kong man and infected his son in February. The father's illness deteriorated into pneumonia before he died.

But the government has said the new virus is not H5N1, which killed six people in Hong Kong in 1997 when it jumped mysteriously from bird to human, sparking fears of an epidemic.

PHOTO CAPTION

Medical staff wear protective masks at Hong Kong's Prince of Wales Hospital where a mystery killer pneumonia affected patients are taken care of March 16, 2003. The World Health Organization warned of a 'worldwide health threat' as the killer pneumonia spread from east Asia to other parts of the globe. (Bobby Yip/Reuter