Canada has responded angrily after the World Heath Organization (WHO) listed Toronto with Beijing and China's Shanxi province as places travellers should avoid because of the danger of Sars.
Some travellers in Canada are concerned about the virus
The country's health agency has written to the WHO to challenge the advisory, with Health Minister Ann McLellan calling it inappropriate.
Canada has reported its 16th death from Severe Acute Respiratory Syndrome. It is the only country outside of Asia where people have died of the pneumonia-like illness.
The WHO is to hold a news conference in Shanghai - which has only reported two cases of the disease - on Thursday.
A two-week closure of all public schools in Beijing begins on the same day as China belatedly moves to fight the disease, which originated there.
The decision will affect more than 1.7 million children.
Also in Beijing, the 1,200-bed People's Hospital of Peking University has been sealed off by authorities, because of multiple sars infections there. Staff and patients cannot leave and no-one is allowed to enter.
The WHO had already warned against travel to Hong Kong and China's Guangdong province, the places hardest hit by the deadly virus.
Challenge to WHO
Canadian officials have said that it is wrong to lump the country's main business centre in with those places.
"There is no evidence of casual transmission of the disease in Toronto," government health officer Dr Paul Gully said. "We challenge the WHO's assertion that Toronto is an unsafe place to visit."
KNOWN DEATH TOLL
Hong Kong: 105
Source: Latest WHO figures
Canadian officials say all the cases in the country can be linked to a single cluster of health workers.
The WHO says the disease was passed from Canada to another, unnamed, country.
The organisation is helping to organise an international meeting on Sars in the Canadian capital Ottawa next week.
More than 250 people have died of the disease worldwide, according to the WHO.
Its travel warning will be active for at least three weeks - double the maximum incubation period for Sars, he said.
Speaking in Rome, WHO Director General Gro Harlem Brundtland said the spread of Sars was "a challenge to everyone".
She said Sars was "a new virus disease, a new type, more malignant" and that "every country has to be prepared".
Beijing authorities also announced on Wednesday they plan to quarantine people exposed to Sars and restrict access to buildings where there are infections.
Nine more deaths were announced in mainland China on Wednesday, including seven in Beijing, taking the total to 106 deaths among 2,305 cases.
Schools are closing in Beijing, affecting 1.7 million pupils
Shanxi is one of the worst-hit provinces in China and was among the first to report the emergence of Sars cases.
Hong Kong, which has also been hit heavily by the Sars virus, has announced a HK$11.8bn ($1.5bn) economic package to lessen the impact of the outbreak.
The death toll in Hong Kong stands at 105, with the total number of cases at 1,458.
As well as affecting China and Hong Kong, the Sars virus has spread to many other parts of the world, with the total number of cases now put at more than 4,000.
Among other developments:
- More than 100 representatives from the world's airlines hold emergency talks in Bangkok to decide how to tackle the Sars crisis
- Police in Australia are given new powers to round up and quarantine suspected Sars victims
Saudi Arabia, home to Islam's holiest
sites, stops issuing pilgrimage visas to many East Asian countries because of Sars fears
Singapore's prime minister vows to jail "irresponsible" people who violate quarantine laws
Despite having no confirmed Sars cases, Japan announces plans to install a thermal imaging camera at Tokyo's international airport to screen passengers
- Tourism continues to suffer, with Hong Kong-based carrier Cathay Pacific cutting 45% of its flights and Singapore reporting a 70% fall in visitor arrivals
- Insurance companies express fears that no airplane exists to safely repatriate Sars victims in accordance with international
Sars appears to be caused by a new strain of the coronavirus, which may have "jumped" from animals to humans in the Chinese province of Guangdong.
Scientific teams are racing to produce a vaccine, but experts have warned that the process is both difficult and time-consuming.
The Beijing Genomics Institute said this week that the virus was "expected to mutate very fast and very easily".
Even when a vaccine is available, it may only offer limited - and temporary - protection, experts have said.