But a departmental spokesman said the confusion which reigned on that morning was unlikely to occur again.

He said there was now a clear awareness among parents that once red or black warnings were issued, the department would automatically announce the closure of schools.

If children were already at school, or had just left to go to school, parents knew children would be supervised by teachers and staff until it was safe to go home and arrangements were made to collect them.

The spokesman said whenever possible the department would make the first school closure announcement before 6.15 am.

Royal Observatory spokesman Chen Yuk-kwon said the system was working well for schools and the community, with government departments receiving early green and amber warnings in case it was necessary to prepare emergency services.

Regular radio announcements are made during red and black warnings. A red rainstorm warning is issued if 50 millilitres of rain falls in an hour and a black warning follows if 100 millilitres falls in two hours.

In 1992, there were two red warnings and one black warning; in 1993, there were two red and one black; in 1994, there were four red and one black. So far this year, there have been no serious storm warnings.

Unions, however, are concerned workers are confused by the warning system.

Hong Kong Confederation of Trade Unions chairman Lau Chin-shek said that until workers had a guarantee that they would not lose a day's pay when a black rainstorm storm warning was issued, they would continue to endanger their lives.

Mr Lau said many workers could not afford to lose pay, so they would come to work regardless of the weather.

He said most workers on daily wages would not be paid if they did not come to work.