It also demanded that all nurseries, primary and secondary schools install electronic temperature monitors and double check students whose temperatures were found to be higher than 37 degrees Celsius.

Yesterday, 31 more swine flu cases were reported, including 10 in Guangdong, nine in Beijing and five in Shanghai. A total of 328 people have been infected with the A(H1N1) virus on the mainland and 168 of them remain in hospital. No deaths have been reported.

Health officials in Guangdong, the province with the highest number of cases at 73, yesterday urged the public to stay vigilant over personal hygiene as it prepared for a community outbreak. It said at least 11 patients had become infected locally.

Among the 11 community infections, at least four cases are in Guangzhou.

Four Guangzhou schools have infected students, but there have been only six confirmed cases. A student surnamed Wu at Guangdong University of Foreign Studies, who returned from Chengdu on June 9, infected a roommate and a school nurse.

The Centre for Disease Control and Prevention is still unable to determine the source of Wu's infection.

Only one school, Guangzhou Electronic Information School, ordered a class that had one confirmed case to suspend lessons for seven days.

People who had close contact with patients were placed under medical observation.

'Although there are more community cases, we haven't reached the stage where we can call it a community outbreak,' a Guangdong Health Department spokesman said. 'We are at a transitional stage, from previously mainly imported cases to having more and more local infections.

'Our estimation is there will be more cases, in which we are unable to determine the source of infection.'

The authorities, so far, have been unable to determine the sources of two of the local cases.

The Health Department also decided it would stop publishing details of each case; instead it would simplify the daily updates by only providing the number of new infections and the total number of cases.