The Chinese Government has called in a team of experts from the World Health Organisation to investigate an outbreak of a deadly virus which has been spreading across the globe.
Officials are urging people not to panic
The illness, a severe form of pneumonia known as Severe Acute Respiratory Syndrome (SARS), is thought by some experts to have originated in China, where five people died and hundreds were infected.
Internationally a further four people have died and around 200 been infected by the illness, which is being passed on by air travellers.
The WHO, which has described the illness as a "worldwide health threat", issued a rare emergency warning over the weekend, saying that cases had been reported on three continents, with more suspected in other parts of the world.
In the latest cases authorities in Geneva said that two people were in isolation in a hospital after exhibiting symptoms similar to those of the disease, Reuters news agency reported.
A British man returning from Hong Kong has been admitted to hospital with a suspected case - the UK's first.
In Australia two women who had recently travelled to China have been hospitalised with symptoms, French news agency AFP reported, although doctors stressed there was no proof they were suffering from the illness.
The Prime Minister of New Zealand, Helen Clark, told a news conference that WHO experts believed the illness might rival the "Spanish flu" pandemic in 1918 - which killed at least 20 million and possibly double that number.
However, an expert from the WHO played down fears.
Pascale Brudon said: "Today we don't know enough about the outbreak to be able to say that. I would be less alarmed than that."
A British expert says that it is unlikely that the illness is flu - the most frightening scenario for experts.
Professor John Oxford, a world-leading figure in virology, based at Queen Mary's College in London said that the fact that a culprit had not yet been identified was good news.
He said: "If it was influenza, I expect we would have heard this by now. That's certainly rather reassuring.
"This has been smouldering around the Far East for some time - it's not as if it has just exploded, I wouldn't get too worried."
The WHO has warned travellers and airport staff to be on the look-out for signs of the condition. Its symptoms include high fever and breathing difficulties, and it has an incubation period of two to seven days.
The majority of cases so far have been in China, Hong Kong and Vietnam.
The outbreak in the Vietnamese capital Hanoi is thought to have begun last month, after an American businessman travelling from Shanghai infected hospital workers before he himself succumbed to the disease.
The illness is thought to be highly contagious
A Vietnamese nurse who died on Sunday is believed to have given him treatment during his time in Hanoi.
As many as 40 others in Hanoi are thought to be infected.
On Sunday, the WHO said two deaths had been reported in Canada. The two are said to be a mother and child returning from Hong Kong, where up to 100 people have already been taken ill.
In Germany a doctor suspected of having caught the virus whilst in Singapore is currently in quarantine.
There are also reports of suspected cases of the disease in Switzerland, France, Slovenia, Taiwan, Thailand, China and the Philippines.
However the East Asian region is the worst affected by the disease.
In addition to cases reported in Hong Kong and Vietnam, authorities in Taiwan and Singapore have reported cases of the disease.
No figures are available yet from China, but the WHO said the flu-like symptoms of the disease were similar to those of a sickness in the southern province of Guangdong last month which infected 305 people, killing five of them.
"All we can tell you right now is that the disease situation here has been placed well under control," a Chinese Government spokeswoman said on Monday.