Hong Kong may have to impose a lockdown for several weeks that closes all non-essential businesses and largely confines people to their homes, a senior government adviser has said as a top epidemiologist warned of a “third wave” of coronavirus infections.

The threat of stricter curbs came as the mother of a six-week-old boy, previously testing positive, was among 28 new cases on Sunday taking the city’s total to 890.

The baby was confirmed as Hong Kong’s youngest Covid-19 patient on Wednesday, after he was held by a family friend, also a coronavirus patient, who had visited a bar with a history of infections.

Officials also said that more than 200 Pok Oi patients and medical staff who might have been exposed in the city’s first possible case of coronavirus transmission in a public hospital had been tested, with nearly all returning a negative result.

Leading infectious diseases expert Yuen Kwok-yung warned on Sunday of a possible third wave of transmission in the city as mainlanders are gradually resuming work and might travel to Hong Kong.

Hong Kong has since late March banned public gatherings of more than four people, while cinemas, fitness centres, bars, pubs and other leisure venues have been ordered to close for two weeks. Restaurants also have to keep tables 1.5 metres apart.

But Bernard Chan, who convenes Hong Kong leader Carrie Lam Cheng Yuet-ngor’s Executive Council, said tougher measures might be required.

“We could limit restaurants to selling takeaway only. Or we could simply impose a much bigger lockdown across the city, and tell all non-essential businesses to close, so nearly everyone stays home most of the time for a few weeks,” he said on RTHK’s Letter to Hong Kong, noting more residents could be returning to the city in the coming weeks.

Chan said the government was considering relief measures that could benefit most sectors. The billion-dollar anti-epidemic fund might look into subsidising employees’ salaries, he hinted. He also urged property developers to exercise social responsibility and reduce rent

Financial Secretary Paul Chan Mo-po said the public should brace for a long period of uncertainty because it was unclear when the pandemic could be contained.

“Based on the current situation, corporations and individuals should know that the economy may show no signs of improvement in the coming six months, and prepare for contingencies on operations and personal finances,” Chan said in his weekly blog on Sunday.

After recording the first imported coronavirus infection on January 21 from a Wuhan traveller, Hong Kong emerged from a rush of imported cases from mainland China and is now going through a second wave with the return of Hongkongers from overseas, including students.

Following criticism of its initial response, the government has shut down most border checkpoints with the mainland, while international tourists have been barred from entering the city since March.

As business activities in mainland cities resume, Yuen, an epidemiologist from the University of Hong Kong, warned of the potential for fresh outbreaks over the border, which could impact Hong Kong.

“After the second wave [from returning citizens], there could be a third wave from mainland China,” Yuen said, stressing that was still hypothetical.

“This cycle could go on until we have an effective vaccine, or collective immunity in the community reaches about 60 to 80 per cent.”

To cope with the daily rise in infections, the administration was increasing its quarantine facilities, including an additional 1,660 units in Chun Yeung Estate in Fo Tan, according to Chief Secretary Matthew Cheung Kin-chung.

At least 1,000 units at makeshift quarantine sites, including on government land in Penny’s Bay and three holiday camps, could also be rolled out between this month and July.

Meanwhile, labour and welfare minister Law Chi-kwong called on employers to encourage domestic helpers to stay home on Sunday or take their statutory day off on weekdays.

Law stressed it was against the labour laws to ask domestic helpers to work on their rest days. Even if these helpers voluntarily agree to work while staying at home, employees must receive extra pay, he added.

“This is only due to the exceptional circumstances [for domestic workers to voluntarily work on their rest days], and should not be viewed as a precedent or the usual practice,” Law said in his weekly blog.

It also emerged on Sunday that the 122 colleagues of a 46-year-old Kowloon police sergeant who was confirmed as infected on Saturday would be sent to Chung Yeung Estate in Fo Tan for isolation, with three of them showing upper respiratory symptoms, health authorities said on Sunday.

Nearly all members of West Kowloon’s elite anti-riot squad were on Saturday ordered into quarantine by top brass in fear of Covid-19's spread within their ranks.