The World Health Organisation doctor who first identified the deadly pneumonia virus which has killed at least 55 people worldwide has died.

The number of people infected with the Severe Acute Respiratory Syndrome (SARS) rose sharply in Hong Kong, where the virus is most prevalent: 45 additional cases were reported yesterday.

But fears about the virus have spread in Singapore, where cinemas and shopping malls were deserted yesterday. Taiwan joined Hong Kong and Singapore in quarantining people at home if they had been exposed to the virus.

Nearly 1,500 people have been infected around the globe, after the virus first showed up in China and was subsequently carried to other parts of Asia, Europe and the United States by travellers.

A number of countries have urged their nationals to put off non-essential travel to China, Hong Kong, Singapore and Hanoi. But Vietnam, where the virus has killed four and infected 62 people in Hanoi, says it is no longer a threat.

In an effort to rein in the disease, Taiwan ordered a quarantine late on Friday on some 240 family members and friends of its 10 patients battling the respiratory disease.

"All the people related have been cooperative. Everybody is scared," said a Department of Health official. Those in quarantine will have to stay at home for up to a fortnight or face a fine of up to £5,700.

Outside mainland China, infection numbers are highest in Hong Kong and Singapore.

Singapore, which has nearly doubled the number of people under quarantine to over 1,500, released the names of 18 people it wanted to locate after they shared a flight with a sick woman.

Struggling with its worst health crisis in half a century, Hong Kong was bombarded with yet another sharp rise in the number of infections yesterday, to 470 from 425 a day ago. The city is also tracking down hundreds of people who may have been exposed to the virus on at least three Hong Kong-linked flights, and one of its top health officials delivered a chilling warning.

"We've never ruled out the possibility that the disease might be airborne," said the director of health, Margaret Chan. An airborne virus spreads more quickly than one carried by droplets.

Scientists say the virus is a new strain from the family of coronaviruses, which is the second leading cause of the common cold.

Airports are screening passengers to sieve out those showing symptoms of the disease, which include chills, high fever and breathing difficulties.

The disease has killed 34 people in mainland China and infected over 800, although authorities say the situation there is now under control. Eleven are dead in Hong Kong, four in Vietnam, three in Canada and two in Singapore. The WHO doctor is the latest victim.