Four public hospitals' emergency units exceeded their full capacity last week amid a surge in flu cases, the Hospital Authority announced yesterday.
More than 500 temporary beds are being added to wards to meet the increase in patient numbers, which are expected to rise steadily over the next week as the winter gets colder.
On announcing the response measures yesterday, Dr Lee Koon-hung, chief manager of the authority, said: "The number of influenza cases we detected over the past few weeks has displayed an increasing trend, but it has not reached a serious level.
"The hospitals are ready to roll out their response measures gradually to meet with the demand, which usually comes one week after a particularly cold period," he added.
Lee said the response plan meant doctors would have to call off their winter vacations to be on duty, and in-patients will have to overflow to less pressured wards.
According to data from the Centre for Health Protection, private doctors reported 33 cases of influenza-like illnesses per 1,000 consultations during the first week of this month.
That number increased to 35 throughout last week, and is expected to rise again in the coming seven days. The level is considered to be alarmingly high when it reaches 40.
Last week, the Prince of Wales Hospital in Sha Tin saw an occupancy rate of 110 per cent and Queen Elizabeth in Jordon saw 108 per cent, while Princess Margaret Hospital and Tuen Mun Hospital each had an occupancy rate of 103 per cent.
"We usually [have] two months of high flu infection during winter, but there was an exception last year as there was a small mutation in the influenza virus, which made it last longer.
"It is hard for me to predict how long the peak season will last this year," Lee said.
He warned the surge in demand was likely to add an extra burden to public hospitals, which have already seen an increase in their overall workload this year.
Daily visits to public accident and emergency units in the city jumped by 8 per cent, from an average of 5,800 to 6,500 this year. One busy day saw 7,700 visits.
The same trend was mirrored at other high-pressure in-patient wards, as admissions to pediatric departments increased by 23 per cent, and internal medicine departments saw a 12 per cent rise in patient footfall.
Non-urgent admission and non-urgent surgery will be reduced to allow the redeployment of beds and staff members.
But urgent treatment, such as cardiac or cancer surgery, will not be affected.