The deadly pneumonia, which is spreading across the world, could be more contagious than previously thought, an expert has warned.
A Toronto nurse takes precautions
Hong Kong, which has been hit hard, has established quarantine camps in an effort to try to contain the spread of the disease.
And at Singapore airport, nurses monitored passengers for signs of the illness. Seven were sent to hospital because they showed symptoms of the pneumonia.
The illness, dubbed Severe Acute Respiratory Syndrome (SARS), has so far killed 62 people worldwide, and infected 1,800.
Initially it was thought that the illness could only be spread by close contact.
But Dr Hitoshi Oshitani, a World Health Organization (WHO) expert, told the BBC that this was not necessarily the case.
He said: "In most cases infection occurs by close person-to-person contact, but there are several cases now that we cannot explain by this model of transmission."
He stressed that SARS was more contagious than the deadly Ebola virus.
"Ebola is not highly contagious in terms of human to human transmission. And we know how to prevent that.
"But this is a new disease. We still don't completely understand the means of transmission."
More cases of SARS have been reported. Hong Kong health chiefs annouced 75 new cases on Tuesday, bringing the total in the territory to 685 cases and 16 deaths.
More than 200 cases have been reported among residents in an apartment block in urban Kowloon.
Health chiefs initially placed the remaining residents of the Amoy Gardens complex in quarantine to try to block further spread of the disease.
But on Tuesday when it became clear this strategy was not working, they began to move residents out to disease quarantine centres set up holiday camps.
Hong Kong Health Secretary Yeoh Eng-kiong said the fact that most of these cases were from the same two apartment units on several floors of the building, raised the possibility that the virus was spreading vertically.
However, a rumour that the entire territory was to be declared an "infected area" has been dismissed as a hoax.
Other developments on Tuesday included:
The first suspected case reported in Australia, a British tourist who has recovered and returned home.
The first three suspected cases reported in Indonesia.
A hospital in Ipoh, Malaysia said it had quarantined several patients suspected of being infected for several days.
Three new cases reported in Singapore, where nurses screening arriving air passengers found seven sick enough to send to hospital.
SARS is thought to have originated in southern China, but has spread to many other countries, including Vietnam, Taiwan, France and Germany.
China 806 cases (34 deaths)
Hong Kong 685 (16)
Singapore 92 (4)
Vietnam 58 (4)
Canada 129 (4)
Canadian health officials said on Monday they had seen 31 new cases.
French authorities are the latest to advise against travel to Hong Kong or mainland China.
Last week, the United States, Canada, the Republic of Ireland and Australia also issued advice to cancel or "re-consider" trips to the affected regions.
China Airlines, Thai Airways, Cathay Pacific and Dragonair have cancelled or reduced flights.
And stock markets in Asia registered big falls amid fears that the outbreak would damage local economies.
The WHO says that 11 laboratories worldwide are trying to identify the virus responsible for the disease.
The US Centres for Disease Control says SARS is caused by a Corona virus from the same family as that which causes the common cold.
The Pasteur Institute in France has drawn a similar conclusion from its analysis of samples.
The WHO says that SARS outbreaks have effectively been contained in Vietnam, Singapore and Canada.
It has highlighted the main areas of continuing concern as Hong Kong and China's Guangdong province.