Education Secretary Arthur Li also told a news conference he was ordering about 180 children with family members infected with the severe acute respiratory syndrome (SARS) to stop attending classes for a week from Monday.

Officials say five schools have already been ordered closed.

School children or staff with sick family members in the future should also not go to school for a week, he said.

But he stressed the 180 children with sick family members were not, at present, sick themselves.

Local health officials had earlier said six children were infected and five of them went to school. Li said all the sick children had contracted the disease from family members, and there had so far been no transmission between schoolchildren.

"More children will be infected in the coming week," Li said, without elaborating. "We believe with these measures, we can prevent the spread of the virus in schools."

The disease is believed to have infected about 400 people globally and 13 victims have died. Most of the sick are in Hong Kong, where the number of patients has risen steadily.

The education chief said there was no present need to shut all schools, and such a move would only be considered in extreme circumstances.

The government demanded schools to improve ventilation and to educate students about the disease, including warnings not to share lunches or water bottles.