Scientists are uncovering more information about the mystery pneumonia which has killed dozens of people.
The Coronavirus has been identified as the most likely cause of Sars
Over 70 people have now died from Severe Acute Respiratory Syndrome (Sars), and over 1,800 have been infected.
Researchers from the University of Hong Kong said they pinpointed a member of the Corona family of viruses as the likely cause of Sars by identifying tiny fragments of its DNA material in samples from affected patients.
Findings from the Pasteur Institute in France, and the influential Centers for Disease Control in America have also pointed towards as Corona virus as the cause.
Dr Mark Salter, from the World Health Organization (WHO), suggested the virus could be an animal virus, perhaps one normally suffered by pigs, which had in some way been spread to humans.
Normally, researchers would confirm this kind of laboratory finding with animal tests.
But scientists are bypassing that stage in the race to find the cause of Sars so they can concentrate on finding ways of diagnosing, treating and preventing the bug.
The test will help terribly in reassuring us we know what we're dealing with
Professor John Oxford, Queen Mary's School of Medicine
The Hong Kong team have developed a test which can identify the virus's DNA material which would allow doctors to confirm a patient was infected with Sars.
However it could be quite some time before this results in a treatment.
There is currently no antiviral drug shown to be consistently successful in treating Sars, or a vaccine which could be given to prevent it.
But now the cause has been identified, doctors can begin work on preventing and treating the bug.
Until now, doctors have had to test for other potential causes to eliminate them before identifying Sars as the cause.
Dr David Heymann, executive director of Communicable Diseases at the WHO, said most outbreaks around the world appeared to be under control.
Most cases are thought to be spread by sneezing, but he said there other factors could be at work in Hong Kong, particularly the clusters of cases at the Hotel Metropole and an apartment complex.
Dr Heymann speculated the virus could be excreted with body fluids, and spread via the sewerage system, or through water.
But he said there was no evidence air conditioning systems in buildings, or the recirculated air on planes, was involved in the spread of the disease.
He said: "It could even be such a thing as a door handle, where someone with Sars has coughed and left some droplets that are moist and which contain the virus, and then the next person that opens the door gets these droplets on their fingers, touches their eyes or their mouth, and becomes infected.
"As far as we know, it is still that example of the two people sitting by me as being at greatest risk, or someone who might touch the table where I have just put some droplets, or some environmental factor which is carrying these droplets to another person," he added.
Vulnerable 'at risk'
The WHO estimates Sars will prove fatal in around 4% of cases, usually where the person has an underlying condition such as diabetes or heart disease, or a weakened immune system.
But it said that in 90% of cases, people seem to recover around a week after being infected.
John Oxford, professor of virology at Queen Mary's School of Medicine, London, told BBC News Online that, like the influenza virus, Sars was likely to affect the elderly and those with an underlying condition most severely.
Professor Oxford said the test for Sars would give results within hours.
"It will help terribly in reassuring us we know what we're dealing with, thereby trying to calm down people's fears that this is going to sweep the world, which I don't think it is."
"It will also help in regard to containing the spread."