That left intact the city’s run of no locally transmitted infections, now at 18 days.

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The four, who left Hong Kong for Pakistan between February and April, were all asymptomatic upon their return, but saliva samples they gave at AsiaWorld-Expo, near the airport, tested positive.

They had been taken for 14 days’ compulsory quarantine at an isolation centre on Chun Yeung Estate in Fo Tan. The youngest among them, an 11-year-old boy, was the nephew of another of the four, aged 40. The pair met over a meal while they were in Pakistan.

Thousands of city residents have found themselves stranded in South Asian countries under lockdown. Last Thursday, 319 Hongkongers stuck in Pakistan were brought home on a government-chartered rescue flight. They were also taken to Chun Yeung Estate for quarantine.

Separately, a 36-year-old former coronavirus patient, who had been discharged, has tested positive again, according to Dr Lau Ka-hin, the Hospital Authority’s chief manager of quality and standards, though he added that the man was not thought to be infectious. He is the 10th patient to be hospitalised for tests having been initially discharged.

Lau said 12 more patients had been discharged in the past 24 hours, taking the total number of coronavirus patients discharged to 944.

Since the contagion began early this year, there have been four virus-related deaths in the city.

Hong Kong has large South Asian populations. According to the 2016 census, 33,000 residents were ethnically Indian, and 18,000 Pakistani.

Some 2,000 Hong Kong residents have sought government help while stranded in Pakistan, and 3,200 are still stuck in neighbouring India, a country whose outbreak Chuang said local officials were “worried about”.

The first government-chartered rescue flight from India is expected to depart New Delhi as early as Saturday, a source familiar with the arrangement said.

“Each returnee will have to pay about HK$8,000 (US$1,030) to travel back on the chartered flight,” the source added.

The city government was discussing the details with the central government’s Office of the Commissioner of the Foreign Ministry in Hong Kong, the Chinese embassy in India, and the Indian consulate in Hong Kong, according to the source.

“The exact number of people who can board the flight will depend on the type of aircraft arranged by the relevant airline and the distance between each passenger,” the source said, adding that fewer than 300 passengers were expected.

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All returnees from India will also be sent to Chun Yeung Estate for 14 days.

On Wednesday, a CHP committee set up to combat emerging infectious diseases recommended discharging all patients found to have antibodies against the virus.

Earlier, only those in good clinical conditions, who had tested negative twice consecutively, 10 days after the onset of symptoms, could be discharged.

Chuang said evidence had shown the virus would usually subside 10 days after the onset of symptoms. However, some patients still tested persistently positive, due to the sensitivity of the test.

Lau said public hospitals would make corresponding arrangements to catch up with the new recommendation and discharge patients.

Additional reporting by Gary Cheung