Officials who had imposed Hong Kong's harshest measures four months ago to gain control of the pandemic are reinstating some of the tough rules, after a relaxation saw a new wave of the Covid-19 outbreak move towards its peak.

To curb the flow of people, from tomorrow till Dec 23, dine-in services will be stopped between 6pm and 4.59am the following day, with the cap on patrons per table during dine-in hours to remain at two.

Businesses such as gyms, sports centres as well as beauty and massage parlours will also be closed.

Banquets will have to cut capacity from a maximum of 40 patrons to 20, while more civil servants are to work from home.

Hong Kong recorded 100 new infections yesterday, bringing its total to more than 7,000 with 112 deaths. Of the new cases, 95 are local and 27 have unknown sources.

Health officials noted that just in the past two weeks alone, there were 1,074 new cases, and over 90 per cent are local.

They said there are now at least seven clusters with more than 10 cases, including the dance club cluster - which started three weeks ago - that now has about 650 patients.

Secretary for Food and Health Sophia Chan said at a briefing that the government now has the power to seal off areas hit by Covid-19 for up to seven days so that tests can be carried out on those affected. Health officials will decide which areas are to be cordoned off and for how long. Food and basic necessities will be given to those affected.

Officials have repeatedly warned that there is a greater number of younger patients in critical conditions this time round.

At the briefing, they said 38 patients are in critical condition while 46 are in serious condition as at yesterday, while 78 per cent of intensive care unit (ICU) beds were filled.

Earlier in the day, Chief Executive Carrie Lam noted that before the latest wave hit, critical cases had fallen to a single digit and most of them were elderly.

"More ICUs have to be mobilised. Of the critical cases, six are under the age of 60 and two are under the age of 50. For serious cases, nine of them are under 60 and two of them are under 50.

"From the observation of experts and our observation, it seems that the situation is more complicated, much, much more than the last one, because we're talking about different people of different jobs living in different districts all over the territory," she said.

The decision to reimpose tough rules came as the city's streets remained mostly busy, with people going about their daily routine.

The closure of leisure spots, such as cinemas, karaoke lounges, bars and pubs is among the few hints of the pandemic's impact, as is the shuttering of eateries by 10pm.

Over the weekend, checks by The Straits Times showed many people doing a spot of Christmas shopping. Some were trying to snag Christmas trees, whose prices have gone up as celebrations are destined to be at home with party rooms' forced closures. Many families were out enjoying the good weather with picnics in parks.

Professor Ben Cowling, an infectious disease expert from the University of Hong Kong, said he is more concerned about indoor crowds than outdoor gatherings.

"It will be important for people to modify their behaviours again if we are to get over this fourth wave soon. Social distancing has been vital in bringing our previous waves to an end," he noted.

From Friday, fines for breaching social distancing rules will be raised to HK$5,000 (S$862) from HK$2,000, among other previously mandated measures such as a public gathering cap of two.

Officials are also mandating that specific groups undergo free tests, such as those in the dance club cluster and, most recently, taxi drivers who plan to work from Christmas through to late next month.

Dr Leung Chi Chiu of the Hong Kong Medical Association noted that besides weak enforcement on the part of the government, private businesses and the public have not adhered to calls to stay home. "The high degree of social mixing nullifies much of the efforts in testing and contact tracing in cutting the transmission links," he added.

Correction note: This story has been edited for clarity.