China has urged people not to travel to the vast countryside, which the World Health Organisation said may see big outbreaks of the deadly virus.
China has raised the number of SARS (Severe Acute Respiratory Syndrome) cases in Beijing 13-fold in two days.
The Chinese travel appeal, widely published in Tuesday's newspapers, was issued ahead of a long May Day holiday now shortened to five days and as the government became more open about SARS after being accused of covering up cases.
The Education Ministry urged students in Beijing not to go back to their home provinces to prevent the spread of a disease that has killed 225 people and infected 4,000 in 25 countries. But the initial signs were that students were ignoring the appeal.
The WHO representative in China, Mr Henk Bekedam, told journalists it would be "quite a challenge to contain SARS" in China and "I think we're going for a very big outbreak".
Premier Wen Jiabao has admitted the health system is badly prepared for any SARS outbreak in the countryside, where 70 per cent of China's 1.3 billion people live.
Nearly half the world's cases, 2001, have been in China, where SARS first appeared in Guangdong province in November. Hong Kong, which has only seven million people, has reported 1,402 cases.
In Beijing, the number of confirmed cases rose to 482 on Monday from 339 on Sunday and 37 the day before. The city also reported 610 suspected cases on Monday, up from 402 on Sunday. Twenty-five people have died.