The sole untraced case was the construction worker living in Yuen Long, who recently worked on a site at Discovery College in Discovery Bay for four days. Chuang said he was mostly responsible for removing concrete in the area, and did not share meals with colleagues.

But she said ventilation was not good and their work was “quite intense, so we consider the [more than 10] other workers in that construction site as close contacts”.

Fewer than 10 people tested preliminary positive. The official tally of infections now stands at 4,822.

Another elderly Covid-19 patient died, taking the death toll to 90. The authority said a 66-year-old woman suffering from chronic illness succumbed to the disease at Tuen Mun Hospital.

On Monday, the city reported nine cases, matching the figure recorded a week earlier, both marking daily lows since July 3. So far, about 20 per cent of patients have been found to be asymptomatic and not among high-risk groups.

The effort began at 8am sharp, with workers taking samples from residents at 141 collection centres across all 18 districts, despite activists and some health workers calling for a boycott.

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Universal Covid-19 tests will not take away testing capacity from others, Hong kong leader says

Universal Covid-19 tests will not take away testing capacity from others, Hong kong leader says

Dr Tony Ko Pat-sing, chief executive of the Hospital Authority, said it was working towards providing coronavirus testing for all admitted patients, but added there were some difficulties in implementing the measure.

“Unlike most private hospitals, we mainly have emergency patients, and the environment is more crowded and cramped so we need to specially arrange a negative-pressure ward if they need to be tested,” Ko told a radio programme.

“But we do agree that we should try to do it as far as possible.”

He said the most at-risk groups in hospitals were internal medicine patients, comprising about half of the treated population at public hospitals. He said hospitals would try to test all patients as soon as possible after admission depending on the order and number of treatments needed.

What you need to know about Hong Kong’s mass Covid-19 testing

Separately, Secretary for Education Kevin Yeung Yun-hung said that while the community testing scheme was not a prerequisite for allowing pupils to return to school, if more people, including parents, students and teachers, took part in the programme it would create a more suitable environment for reopening campuses.

“As for the long term, we are considering whether we will need to have regular testing in schools,” he said. However, whether the testing would be mandatory or voluntary was still under consideration.

On Tuesday, the Housing Department said that blocks 1 to 3, comprising 1,707 flats, of Chun Yeung Estate, a new public housing estate temporarily turned into a quarantine centre, would be returned to tenants by the second quarter of next year at the earliest. Some tenants started moving into blocks 4 and 5 from last month.

The department said the estate would cease to operate as an isolation site after 2,000 units at Penny Bay’s quarantine centre began operations by the end of this year, according to government plans.

The Housing Authority added that it would strengthen its infection control, and inspect the common drainage system linked to flats with confirmed patients. In future, the authority would also proactively check all common drainage systems in public housing.