The source of infection in 54 cases, or 30 per cent of the recent local caseload, could not be traced, according to the city leader Carrie Lam Cheng Yuet-ngor.

Clusters first emerged in Kowloon East and Sha Tin, expanding to a handful of local restaurants, secondary schools and elderly care homes, as well as public and private housing estates across Hong Kong.

The government on Monday announced the introduction of stringent measures from Wednesday, banning for the first time dine-in services at restaurants from 6pm to 5am the next day, while passengers on public transport must wear masks.

The limit on the number of people gathering in public will revert to four people from 50, while restaurants can now place no more than four to a table.

Evaluating the situation over the past six months, Hui said although Hong Kong had seen sporadic bursts of local cases before, the community outbreak since last week was worrying, as he cited two reasons for the latest spike.

“Two mistakes the government have recently made have caused the community outbreak: the exemptions for tests and quarantine for airline and cruise crews which brought many asymptomatic cases into the community, while a total lift of the eight-people rule in restaurants last month was also a failure,” Hui, a respiratory medicine professor, told the Post.

The government last week amended its policy to impose mandatory testing on airline and cruise ship crews, who were previously exempt in what Hui saw as a loophole in the fight against community contagion.

Upon arrival in Hong Kong, foreign domestic workers must also be quarantined in hotels, at their employers’ expense.

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Fourteen cases – including five airline crews and nine seamen – have been confirmed positive since last Wednesday, according to official figures.

Echoing Hui’s view, Peiris, from HKU, said the city needed to stop the virus being repeatedly brought into the city either via imported cases who were under home quarantine or those exempted from testing on arrival, such as airline crews and sailors. He called for a review of quarantine procedures in that area.

Health officials earlier said the latest spike had put increasing pressure on both the public health care system and the city’s quarantine capacity, with a major facility in Fo Tan to be returned to public housing tenants next month.

Hui suggested that some of the returnees from high-risk areas such as India, the Philippines and Pakistan should be put into quarantine centres, while hotels should be used for that purpose for other returning residents or crews, as a form of home quarantine.

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A previous plan to use AsiaWorld-Expo to isolate recovering patients or those with mild symptoms should be reconsidered as well, he said.

Earlier in March, sources told the Post that the government had been preparing to transform exhibition centres into “temporary hospitals” if the public health care system became overwhelmed by the daily surge of imported and community-spread infections.

HKU’s Yuen, who is also a government adviser, agreed further isolation facilities were needed if the infection numbers did not come down within one or two weeks.

“The excess number of mild cases would have to go to non-hospital isolation facilities for monitoring,” he said.

Yuen added that the severity of the outbreak could be determined by the number of local cases, the percentage requiring intensive care unit services, and mortality rates.

Coronavirus immunity may not last more than a few months: study

Sridhar, a clinical assistant professor from HKU's department of microbiology, also said there was a need for dedicated facilities to care for mild or asymptomatic cases, with an urgent transfer service in place to send patients to acute hospitals in the event of clinical deterioration.

Moving forward, both Hui and Peiris agreed that the coronavirus would be a long-term struggle, requiring repeated cycles of “suppress and lift” until a vaccine was ready.

“The only way the outbreak will be naturally contained is when there is a sufficient proportion of the population that has acquired immunity,” said Peiris, adding the only way that would come about was through large numbers becoming infected and recovering, or under a vaccination programme.

“This means our ‘suppress and lift’ will have to continue until we can acquire immunity, and the only way that can be acquired relatively quickly and painlessly is via vaccination when vaccines become available. This may not be much longer, maybe by the end of 2020,” Peiris said.

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Until then, he said Hong Kong had to follow suitable social-distancing measures as well as tough precautions on personal hygiene.

“After we have got through the third wave of outbreak, the restrictions for public gatherings and restaurants should not be lifted right away. We should always take a gradual approach,” said Hui.

Peiris added that a positive for Hong Kong was that the city had experience from other health crises, such as with the severe acute respiratory syndrome (SARS) in 2003, as well the previous waves of Covid-19.

“A potential weakness is “fatigue” among the public. I think we need to communicate the importance of these measures. The alternatives are clear from those states who have failed to control the virus and the price that is being paid in human suffering and death and also, ultimately economic impact,” he added.

“This is not a choice between the economy and health. Without health, there will be no ‘economy’ anyway.”

Meanwhile, retailers and restauranteurs braced for even more turbulent times ahead.

Hong Kong Retail Management Association chairwoman Annie Tse Yau On-yee, said cutting rent was the key to saving the devastated sector.

Simon Wong Ka-wo, president of the Hong Kong Federation of Restaurants and Related Trades, struck a sombre tone, saying: "Only when we manage to contain the outbreak will we be able to find a way out to revive the sector."

Additional reporting by Cannix Yau