The Centre for Health Protection has confirmed 20 institutional norovirus outbreaks affecting 204 people in December so far, compared with 12 outbreaks affecting 102 people in November.

Surveillance systems at elderly homes have indicated an upward trend in acute diarrhoea since early December.

The centre's Consultant for Community Medicine Dr Thomas Tsang said winter is historically the peak season for norovirus outbreaks.

Good personal, food and environmental hygiene are vital in preventing the spread of the disease. An effective preventive measure is to eat well cooked food as heat effectively destroys the virus, he said.

Japanese health authorities say there has been an early increase of norovirus outbreaks since October. The activity of infectious gastroenteritis in Japan is the highest in the past 10 years during the period.

Dr Tsang said: "We have contacted our Japanese counterparts for more updated information and are closely monitoring the situation."

The department has informed the local travel industry about the outbreaks in Japan and reminded travel agencies and travellers to guard against the disease by maintaining good hygiene.