Yuen agreed that Hong Kong could double the number of samples taken daily, saying that would make it easier for authorities to accurately gauge the outbreak’s development, although he said it was unlikely the coronavirus would disappear completely.

“Singapore and South Korea are doing a better job,” Yuen told the radio programme.

“Basically in Singapore when someone has a fever or cold symptoms, a test will be done, followed by plenty of tracing and isolation. In Hong Kong, the number of tests being done is highly inadequate.”

Yuen said more tests were needed especially with Hongkongers letting their guard down in recent weeks.

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Rather than staying at home, people had been going out in greater numbers, some without masks, making the streets and restaurants busier, he added.

“Hong Kong can continue to defend itself until the summer, if we can do more tests and identify the invisible chains of infection in the communities,” he said.

Yuen expected the mortality rate of Covid-19, the disease caused by the coronavirus, to decrease in Hong Kong in the summer as the weather warms up.

“When the temperature is high enough, the lifespan of the virus will be short, and the number of viruses that we can get can be relatively low,” he explained.

“At that time, even if 20 per cent of the population gets infected, the mortality rate … could be lowered to 0.1 per cent, just like a seasonal flu. This may sound scary, but it will happen naturally.”

Yuen urged Hong Kong authorities to put everyone returning from Britain and the US under home surveillance, as he expected the number of infections there to rocket in the next four to eight weeks.

“I believe that some Western countries have been adopting a so-called, very traditional, old-style approach,” he said.

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“In the past, when a child had measles, parents would take their own children to a party with the child, so everyone got infected.

“But you can only use this kind of so-called herd immunity to control a disease when the death rate is very low.”

The microbiologist said it was too risky for Hong Kong to adopt a similar approach to immunity, especially when the mortality rate for Covid-19 stood at 1 to 3 per cent.

“In two to three months, 20 to 30 per cent of the population can become immune. But the biggest danger of this approach is that your medical system could be paralysed,” he said.

“A lot of elderly people might not get appropriate treatment, and some doctors and nurses could die because they remained busy after being infected. This could cause much public fear.”

Exco member Lam said Hong Kong authorities had been closely monitoring the situation, especially in the US, Britain, Canada and Australia.

He conceded that tighter health measures would ramp up pressure on the city’s quarantine centres, as well as government officers responsible for contacting those under home surveillance.

From Tuesday, anyone arriving from the Schengen region, an area comprising 26 European states where people can move freely, will have to undergo mandatory self-quarantine for 14 days.

Countries including France, Germany, and Denmark would be subject to the restrictions, but not Britain which is outside the Schengen zone.