As scientists scramble to unravel the mystery of severe acute respiratory syndrome, a sense of crisis is spreading even faster than the illness itself.

People in Hong Kong are buying surgical masks by the thousands. Hospitals have closed in Canada, a jetliner was briefly detained and inspected in California, and the Panama Canal dispatched inspectors to check ship crews for symptoms.

A hoax that Hong Kong had been declared an "infected city" prompted panicked people to rush out and stock up on food. In Thailand, authorities turned away a French warship en route from Singapore, which has reported cases.

Economists warn it could batter Asia's economy as manufacturers temporarily shut down, consumers avoid malls and restaurants and tourists to stay away.

Severe acute respiratory syndrome, or SARS, has now sickened more than 2,200 people worldwide and killed at least 78. Some of the alerts cropping up in infected countries are real, some aren't; but fears about the disease are gaining momentum.

In Hong Kong, authorities used barricades and tape to seal 240 people inside their infected apartment building. The next night, they were put in quarantine camps.

Hong Kong has become something of a masked city, with hundreds of thousands of people putting them on around town - some sporting creative designs such as cartoon characters or bright floral patterns. The World Health Organization recommends masks only for those in contact with victims.

"If you put on a mask but don't fasten your seatbelt in your car, that's upside down," said Dr. Guenael Rodier, WHO's head of surveillance and

response.

Doctors and nurses in Singapore have donned germ-warfare suits to get closer to patients.

The Geneva-based WHO warned people on Wednesday to avoid travel to Hong Kong and China's Guangdong province, where most of the mainland's deaths occurred. But many places have already been screening travelers.

Meanwhile, a medical team landed on Thursday in southern China for the first international inspection of the region believed to have spawned a deadly flu-like illness, while jittery governments from Hong Kong to Thailand toughened enforcement of quarantine rules to curb the disease.

After days of waiting, four World Health Organization experts arrived in China's Guangdong province to investigate how severe acute respiratory syndrome, or SARS, was born - and how it began its worldwide spread.