“There are reports of outbreaks in prisons overseas,” she told a press briefing. “We are a bit concerned whether there’s any chance of transmission although he only stayed there for one or two days.”

Chuang said the man arrived in the city last October, and was sent to the holding centre after he was found to have overstayed his visa during a police identity check on Sunday.

More than 300 detainees and 200 immigration officers would now be tested.

Three men who shared a cell with him and five immigration officers who conducted checks while his mask was removed were deemed to be close contacts and would be quarantined.

The Immigration Department said the Thai man and the three others in the same cell did not make contact with any other detainees or people while waiting for their test results.

The patient, who lived with a friend in Tsuen Wan, was believed to have contracted the virus in the community. Chuang said police would help with contact tracing as the man was not cooperating.

“The man was not living in the centre before he was tested positive,” she said. “As of why we have to test so many, normally when someone gets infected in a company, we test the entire company.”

Tests are carried on everyone newly admitted to the centre, which holds immigration detainees awaiting repatriation or deportation. People sent to prison undergo quarantine for 21 days before being placed in cells.

Chuang said 1,400 detainees had been tested and the man was the only positive case so far.

Previously, an office worker at Lai Chi Kok Reception Centre and a lawyer who visited the facility and Stanley Prison were confirmed to have Covid-19.

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Human rights campaigners and politicians had earlier raised concerns about conditions at the Castle Peak Bay centre. Twenty-eight detainees had joined a hunger strike, now in its 52nd day, at various stages.

A concern group on Wednesday released survey findings from 100 respondents, mainly ex-detainees and their family members, in which 48 per cent complained of insufficient medical care in the facility.

But the Immigration Department previously said claims of inhumane treatment were unfounded. It said it has provided medical examinations, exercise, personal hygiene and other arrangements, adding it had monitored hunger strikers’ health and provided tea and milk to them.

04:53

Jobless struggle to make ends meet in Hong Kong as city battles coronavirus and recession

Jobless struggle to make ends meet in Hong Kong as city battles coronavirus and recession

All but three of the latest infections were locally transmitted, including 15 linked to previous cases and eight of unknown origin. The overall tally stands at 4,586.

The three imported infections were all from India, and came just a day after local authorities banned Air India flights for two weeks after positive cases were detected among arrivals from the country despite them testing negative before flying. Two of the cases flew in on Friday and one on August 4.

The number of daily infections was the lowest since July 15, when 19 cases were reported.

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But another elderly patient died – an 86-year-old resident of Choi Fai Estate, taking the number of fatalities to 72.

Among the newly confirmed cases was a security guard who worked at Kwai Tsing Container Terminals. Authorities have collected and tested 3,400 samples from 8,000 workers at the port so far.

The Labour Department said 3,800 specimen bottles had been given to domestic workers staying in boarding facilities and 1,519 specimens had been tested.

The universal Covid-19 screening scheme, announced by Chief Executive Carrie Lam Cheng Yuet-ngor on August 7, was likely to begin on September 1, according to doctors’ groups which attended a meeting with officials over the matter on Tuesday.

Medical Association president Dr Gabriel Choi Kin said the government did not say why the start of the testing was postponed from the original date around the end of August.

He said health minister Professor Sophia Chan Siu-chee had revealed that about 2,000 people had agreed to help with the scheme, but it was not clear how many were doctors, nurses or other health care professionals.

Choi said the association had so far recruited about 100 doctors for the scheme. “It is not a too enthusiastic number,” he said, adding that he had not analysed the reasons behind the response rate.

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Dr Henry Yeung Chiu-fat from the Hong Kong Doctors Union said the screening was likely to last for around two weeks. He said the union had recruited up to 100 doctors to help, and the recruitment was still going on.

A government spokesman said the authorities were following up on the launch of the scheme and the details were still under discussion.

The third wave of the pandemic has forced the cancellation of annual events or seen them moved online. The Hong Kong Tourism Board said the four-day Wine & Dine Festival, expected to run from October 29, would be held online this year.

The Hong Kong Cyclothon, originally slated for November, has been cancelled.

Additional reporting by Christy Leung