According to preliminary investigations, all nine individuals visited the premises after 5pm last Monday, and some started to show symptoms on Wednesday.

Authorities said they would inspect the site and examine whether a superspreading event could have taken place.

“Some people said they were only there for 10 minutes to get something … we need to investigate whether some customers took off their mask and ate there,” said Dr Chuang Shuk-kwan, head of the Department of Health’s communicable disease branch. “If some individuals were highly infectious, they would spread the coronavirus even when they wore a mask.”

Another case was also tied to cluster at a snooker hall in Hung Hom, taking the total to 13, while two more infections emerged at Sai Wan Estate in Kennedy Town, bringing the overall number to 24.

But the most worrying cluster remained the one linked to Sky Cuisine restaurant in Sheung Wan, which grew from 41 to 52 cases, comprising 20 families. Health officials said they feared the virus had spread across the entire eatery.

Chuang admitted infections were rising, but she insisted the situation remained stable, pointing to the reproduction rate of the virus that estimated the number of people a patient could infect. An epidemic will worsen if the number is greater than one and vice versa.

“The real-time effective reproductive number is 0.8965,” she said. “But if we talk about March, it was between three and four … It’s worrying if it’s higher than one, as it means one patient can infect more than one person … But if it’s smaller than one, the epidemic situation remains stable.”

When asked whether the government was drawing up contingency plans in response to the warning about an approaching sixth wave made by Professor Gabriel Leung at HKU, Chuang said the calculation was only a mathematical model.

“For social-distancing measures, I think we have to take into consideration the overall outbreak, not just how many cases there are,” she said, adding it was difficult for health authorities to track hundreds of invisible transmission chains because most cases did not exhibit symptoms.

Hong Kong could be hit by sixth Covid-19 wave in 2 weeks, top health expert says

The Post reported on Saturday that Leung told a university forum that the next wave of infections could hit the city in as little as two weeks.

“[Hong Kong’s] daily reported cases have remained static around 300 for the past couple of weeks,” he later posted on Twitter on Saturday. “We are on the cusp of a potential sixth wave if things tilt in the wrong direction slightly.”

While vaccination could prevent severe complications and death, it “[does] not work nearly as well against infection”, he noted.

Infectious diseases specialist Dr Joseph Tsang Kay-yan said Leung’s model provided some data about how the pandemic might develop in Hong Kong. But he also did not see the need to tighten social-distancing rules unless infection and hospitalisation rates increased among high-risk groups, such as children and the elderly.

Tsang, co-chairman of the Medical Association’s advisory committee on communicable diseases, said the city had built up a barrier or gained “natural immunity and vaccine immunity” from the previous months-long outbreak.

“It depends on whether the upsurge will die out soon or if it reaches a new plateau,” he said. “Now, we lack a good method to measure the full picture regarding the infections as the daily cases are just the tip of the iceberg.”