A mysterious form of severe pneumonia is continuing to claim more victims as US scientists announce a possible breakthrough in the search for the culprit.
The illness is creating widespread concern
The World Health Organisation now estimates that 487 people in 13 countries world-wide have been infected with the disease, dubbed Severe Acute Respiratory Syndrome (SARS) in the past two weeks.
US researchers believe the illness may be caused by a new, more virulent version of the virus that causes the common cold.
So far 17 people are thought to have died from the disease, with another five deaths in the Guangdong province of China - where authorities suspect the outbreak started - closely linked.
Twenty-six new cases have been identified in Hong Kong, bringing the total in the territory to 290.
They include nine people who returned from a holiday in Beijing last week.
There's very strong evidence to support coronavirus as the cause
They are thought to have contracted the disease on a flight to the Chinese capital from a Beijing man who fell on his return to China after visiting his brother at a Hong Kong hospital.
Ten people from the territory have so far died from the disease, which is reported to have created a climate of fear, with many people opting to wear masks.
It is thought that ten hospitals and a number of schools have been infected.
In Vietnam, a nurse and a gynaecologist who worked at the Vietnam-France Hospital in Hanoi died from the illness on Monday afternoon.
Countries with reported cases
China (including Hong Kong and Taiwan)
Republic of Ireland
Both had direct contact with Johnny Chong Chen, the man who is thought to have brought the bug from Hong Kong to Hanoi.
The first case has also been reported in France. The man who arrived in the country on Sunday had been working as a doctor in a French hospital in Hanoi, Vietnam.
The 65-year-old heart specialist is being treated at a hospital in Tourcoing, northern France, where he is described as critically ill.
A hospital spokesman said: "His condition is stable but he is in danger."
Eleven other people, who have recently returned from Asia and have displayed SARS symptoms, are also under observation in the country.
In Singapore, the Ministry of Health has invoked special powers to keep 740 people under home quarantine in an attempt to try to halt further spread of the disease.
Singapore's Health Minister Lim Hng Kiang told the BBC: "A stronger wall is now created to break the chain of infection".
The number of cases in the city-state has risen to 65 with 12 victims in a serious condition.
The people placed under quarantine are thought to have had close contact with others who have developed symptoms.
If they break the quarantine they will be fined 5,000 Singapore dollars (2,840 US) for the first time and 10,000 dollars for the second offence.
Schools and nurseries have been placed on alert. In one case 200 students from a secondary school were asked to stay at home for a week after a 13-year-old pupil fell ill.
Eleven laboratories in nine countries are working to find a cure for the disease.
However, there has so far been no consistency in their findings.
Scientists in Germany and Hong Kong believe the culprit is a virus belonging to the paramyxoviridae family, members of which cause mumps and measles.
However, US experts from the Centers for Disease Control and Prevention announced on Tuesday that the cause could be a virus from the coronavirus group.
They said tests on tissue taken from infected people had revealed traces of a form of the microbe.
At present, there are three known varieties of the coronavirus. The CDC team suspect that they have discovered a fourth type.
CDC director Dr Julie Gerberding said: "There's very strong evidence to support coronavirus as the cause.
"If it is not the entire cause of SARS, it at least contributes to it."
The WHO has appealed to the authorities in Beijing for more cooperation in tracking down the origin of the disease in China.