Hong Kong's Department of Health took the unprecedented step this morning of ordering all residents of an apartment building to be quarantined at home for 10 days, after a sharp rise in cases of a deadly pneumonia virus in the housing estate.

The move marked a dramatic escalation of Hong Kong's efforts to control the spread of the pneumonia that emerged in southern China this winter and has become the focus of a global health alert. It came after the number of infections in the city leapt by 60 to 530 Sunday, with 36 of the new cases coming from Amoy Gardens housing estate.

"Because of the very special circumstances that we now face, we have no choice but to resort to this exceptional measure," the Hong Kong government said in a statement.

The disease, known as severe acute respiratory syndrome, or SARS, has sickened more than 1,600 people worldwide. Canadian health officials said Sunday a fourth person had died from the disease, bringing the death toll to 59 worldwide, including 13 in Hong Kong.

The apartment complex outbreak, along with other evidence, suggests that in some cases people can catch the disease from indirect contact with infected individuals -- perhaps by walking through an area where someone has recently coughed or sneezed or by touching an object that a sick person recently touched, officials have said.

In a new effort to isolate people who may be in the earliest stages of the disease before they have a chance to spread it to others, Hong Kong officials called upon all close contacts of SARS patients to get checkups at four designated medical centers. They are to repeat those visits daily for an unspecified period to get X-ray exams and other tests to check for the first signs of the disease.

Close contacts are also "required" to stay away from work and school for 10 days after exposure and, to the extent possible, to stay at home, according to a bulletin posted on the health department's Web site. "This measure will help control the spread of the disease and ensure that any close contact of patients who have been infected will be diagnosed and treated early," a department spokesman said.

Weiss reported from Washington.

Passengers from Hong Kong at Taipei's Chiang Kai-shek International Airport wear masks for protection.