A hastily built Sars isolation facility went into operation outside Beijing today, as China reported 11 more people had died from the virus and a further 176 were infected.

The surge in new cases - with 100 people being infected every day in the capital alone over the last week - has taken the country's death toll to 181 and the number of infections to 3,799.

In Hong Kong, hospital authorities today announced eight more deaths and 11 new infections, bringing the local death toll to 170 and the cumulative cases to 1,611.

The latest figures emerged as Chinese health chiefs admitted they had no idea when the virus would be brought under control.

Liang Wannian, deputy director general of Beijing municipal health bureau, told a news conference the pneumonia-like disease has been in the "peak period" since April 21 and that he expected the number of new cases in the country to begin falling within 10 days.

But he stressed it was too early to say when Sars would be eliminated in Beijing - let alone in the country's vast rural areas, where hospitals would be no match for a full-blown outbreak of the mysterious disease.

He said: "My personal judgement is the present high plateau of the number of cases in Beijing will continue for a period of time. Overall the situation in Beijing is stable, and the upward trend has been effectively checked.

"I think it will take a long time for us to eliminate this disease. I believe the number of patients will drop in the future, but it is hard to say when because we don't know a lot about the disease," he said.

The Chinese capital has suffered more than any other city in the world. At least 91 people have died of Sars and more than 1,640 have been infected.

In the country as a whole, Sars has claimed 170 lives and infected more than 3,600 since it emerged in the southern province of Guangdong late last year. Authorities have been forced to shut down schools for 1.7 million students, and close cinemas, karaoke bars and other public places

Authorities in Shanghai have detained 132 people who were protesting about being forced from their homes, after the city imposed a ban on large gatherings to prevent the spread of Sars.

In Hong Kong, health officials said some patients released from hospitals after they were thought to have recovered continued to carry the Sars virus, and some have suffered relapses.

"We warn them not to have close contact with family members, like no kissing, no hugging," said Dr. Joseph Sung, head of the department of medicine at the Chinese University of Hong Kong.

The World Health Organization said China was facing a critical period. "The next few months will prove crucial in the attempt to contain Sars worldwide, which now greatly depends on whether the disease can be controlled in China," the WHO said in a statement on its website.

Doctors say immediately isolating Sars patients is key to preventing its spread and quick treatment may help patients survive.

The Xiaotangshan hospital in northern Beijing, boasting at least 90 million yuan (£7 million) worth of medical equipment, opened its doors after more than 7,000 builders rushed to erect the temporary facility for Sars victims in eight days.