But while some in the sharply divided medical community called for a more “upstream” containment strategy, the city’s leader firmly ruled out the idea, calling it “inappropriate and impractical”.

Her stance was backed by experts including the dean of the University of Hong Kong’s medical school Gabriel Leung, who said the border had never been closed in the past 20 years, even during the height of the severe acute respiratory syndrome (Sars) outbreak and avian flu and swine flu epidemics.

Chinese University professor David Hui Shu-cheong called the suggestion “extreme”.

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But Lam also came under fire over “toothless” declaration forms, with Hui saying they only served as an enforcement tool because many people would lie to enter the city.

On Sunday, the city’s health care workers and experts mooted several new proposals to close the border.

The Hospital Authority Employees Alliance, a new pro-democracy union representing about 2,000 workers in the city’s 43 public hospitals, went furthest, calling for an indefinite ban on mainland travellers, with a periodic review of the scheme, which would end when the epidemic showed signs of being brought under control across the border.

“A complete ban is now inevitable and logical as the virus has gone everywhere in China now,” he said.

But Law admitted such a ban was a radical idea. “There may be economic losses, but we must put people before profit at this stage,” he said.

The union earlier upped the ante by listing five demands – including the travel ban and a call to halt all non-emergency services to free up more isolation wards at public hospitals – and threatened industrial action and a five-day walkout from February 3 if these were not met.

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Alex Lam Chi-yau, chairman of the Hong Kong Sars Mutual Help Association, a group formed by more than 300 survivors infected in the 2003 outbreak, added his voice to the debate and advocated a 14-day moratorium on mainland visitors, saying the time would be long enough to cover the incubation period of the virus, so new arrivals with symptoms could be detected.

 Dr Arisina Ma Chung-yee, president of the Public Doctors’ Association, also heaped pressure on the government by putting forward a five-point plan, which called for a “vastly reduced flow of people”.  

“We would like to see enhanced border controls on the mainland side too, so they can stop people with fever or other symptoms coming to Hong Kong,” Ma said. “This may be more politically acceptable than a blanket ban.”

On Sunday, Macau ramped up its measures, saying that about 1,100 Hubei visitors in the city needed to return to the mainland or they would be placed in isolation.

Earlier, it announced a “partial border shutdown” by requiring all non-local visitors who had been to Hubei in the past 14 days to produce a medical certificate proving no coronavirus infection. Those without a valid note will be denied entry.

Other medical experts, however, cast fresh doubt on the effectiveness of a travel ban. Top HKU microbiologist Yuen Kwok-yung said he was not opposed in principle to such a ban, but called into question its effectiveness.

“There are many technical issues that may render the scheme ineffective,” he said. For example, many mainland travellers tend to go to Southeast Asia on holiday, then stop in Hong Kong for two to three days to shop. So, are you going to stop all flights from Southeast Asia too?”

The professor added many mainland visitors had already arrived in town during the Lunar New Year break, and many Hongkongers were yet to return from visiting relatives across the border.

“Universal masking and good hand hygiene are the best way to beat the virus, as they can help block infection from even the cryptic patients with no symptoms in the community,” Yuen said.

Dr Tsang Ho-fai, former controller of the Centre for Health Protection, said the ban’s effectiveness was in doubt as goods and supplies still needed to cross the border, and mainland Chinese could arrive through a third country.

But he acknowledged the possibility of some mainlanders coming to Hong Kong hospitals seeking better treatment for suspected coronavirus infections, even risking isolation in the local wards. “This could potentially be a loophole, but we have to wait and see if many people will abuse the system that way,” he said.

While Tsang praised the government’s response so far, saying it had done more than in 2003 during the Sars outbreak by suspending classes even before confirmed contagion in the community, he also acknowledged the concerns of frontline hospital staff.

“I don’t support a strike, of course, because as doctors we have to put patients first. But I think their demands for more resources should be met, such as accommodation requests for overstretched staff who don’t want to go home for fear of passing the virus to their family,” he said.

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Chinese University economics professor Terence Chong Tai-leung also urged caution on pulling up the drawbridge on mainland travellers, saying it could risk as much as 1 per cent of the city’s GDP.

He said: “We have to weigh up the cost of a border shutdown versus the risk posed by a virus outbreak. If the virus is proven to be 100 times more contagious and deadly than Sars, then I think we have a case for a complete lockdown.”