Health Secretary York Chow said the peak flu season was likely to last until the end of April but he stressed there was still no scientific evidence proving the three recent deaths were due to flu.

Hong Kong authorities shut down all primary schools and kindergartens on Thursday, shortly after a flu-like illness was reported in 23 of them.

It was the first time that schools in this Chinese city have been closed over a health scare since the 2003 SARS epidemic that killed almost 300 people in Hong Kong and set off international health alarms.

'If there is not mutation of the strains, we estimate the peak of the flu season may end in the end of April,' Chow told RTHK radio on Friday.

'The three-year-old girl and the seven-year-old boy who died in Tuen Mun Hospital had tested positive for the H1 flu virus, but we also found they had some other illnesses that might have caused their deaths,' he said.

'We also could not find any flu virus in a 27-month-old boy who died.'

Mr Chow said the government was considering free flu vaccines for children under 12 years old, at a cost of about 100 million HK dollars (S$18 million).

The health secretary brushed off complaints from some parents that the decision to close schools had been hasty.

'If we announce the close of all schools one day later, it may cause even more chaos and the situation may worsen' he said. -- AFP