“We are paying great social costs every day to control this epidemic,” he told a radio programme on Wednesday. “Although the tests are voluntary, we hope the public will take part together, for themselves and for society.”

Online reservations for the testing will begin on Saturday, and Hongkongers will be able to choose from more than 100 sites across all 18 districts.

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Sources told the Post that more than 20 government schools, including Queen’s College, had been selected, as well as most of the indoor stadiums in the city, such as Queen Elizabeth Stadium in Wan Chai and MacPherson Stadium in Mong Kok.

Nip said adequate precautionary measures would be adopted for the medical staff taking part in the drive. They will be given training and required to undergo face-fit tests for using respirators. The gloves they use will be thrown out after collecting each sample.

Private doctors’ unions had a meeting with government officials on Tuesday night, in which Henry Yeung Chiu-fat, president of the Hong Kong Doctors Union, said at least two teams would be working in each venue.

Current and retired civil servants will distribute bar codes and sample bottles, while a team of medical professionals will collect the samples.

The authorities said the booths would be closed temporarily for cleaning and disinfection in case someone sneezed or vomited while giving their samples.

Yeung said about 10 partitioned booths would be set up in each testing site. He also said that the government would continue to recruit people for the programme until this Friday, as some areas in New Territories East and West still had a staffing shortage.

Dr Gabriel Choi Kin, president of the Hong Kong Medical Association, who also took part in the meeting, said authorities would provide masks, gloves and protective clothing.

But Adrian Lau Cheuk-yu, a Tsuen Wan district councillor, said many local residents objected to the use of a stadium there as a testing centre.

“The government should stop using sites that are close to residential buildings. Authorities should also provide the location details of all testing centres as soon as possible,” he said, adding that no more than 100 people should be allowed at each testing station every hour.

Separately, Sweden’s Public Health Agency said a faulty test kit made by BGI Genomics, based in mainland China, had returned about 3,700 false-positive results, an error discovered by two Swedish laboratories during routine quality controls.

“People who had mild symptoms or who didn't feel any symptoms at the time of the test received false-positive results,” the agency said in a statement, adding the kit from BGI Genomics could not distinguish between very low levels of the virus and a negative result.

Sunrise Diagnostic Centre Limited – BGI’s joint venture company that will assist in the mass testing in Hong Kong – issued a statement on Wednesday, saying “high positive detection rates brought about by high-sensitivity testing kits is necessary for the prevention and control of the epidemic”.

The company said the “so-called” high positive detection rate problem was mainly due to differences in sensitivity standards in various countries.

The company said high-sensitivity kits would label some asymptomatic carriers, who might otherwise come across as “healthy” during clinical observations, as positive cases. It also said a low-sensitivity test kit might judge the same set of people as negative cases.

“But it would cause greater harm if these infected persons took part in daily work and social activities as ‘healthy people’,” the company said.

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In a separate statement, BGI Genomics said it was aware of reports from a European media outlet regarding “high positive detection rates” from its testing kits and took the matter very seriously.

The rates could be linked to the different standards on sensitivity adopted by various countries, it said, adding high sensitivity was needed to prevent the chance of a false negative. Kits used in Hong Kong had the same specification and the agreement with the Department of Health was aimed at filtering out suspicious infections.

“The Department of Health will then conduct further testing and review cases with ‘preliminary positive’ results followed by a diagnostic report,” it said.

Its kits had undergone rigorous and extensive third party testing and were certified for use in the United States, European Union, Australia, Canada, Singapore, Japan and mainland China, the statement said. They were also contained in the World Health Organisation’s Emergency Use List.

Professor David Hui Shu-cheong, a government health adviser, said the public should not be worried if some false-positive cases emerged from the citywide testing, as every sample found initially positive would be sent to the Department of Health for double verification.

“The mechanism is very stringent,” he said. “The additional test for confirmation gives us an extra safeguard.”

The government said on Wednesday night that under the existing mechanism, specimens that tested positive for Covid-19 in private laboratories were considered preliminary positive. The specimens had to be referred to the Public Health Laboratory Services Branch for confirmatory tests. After the branch confirmed the positive result, the Centre for Health Protection would classify it as a confirmed case.

“It is not uncommon for the branch and the private laboratories to have discordant results using different platforms during the confirmatory process, and it has happened occasionally in the past,” it said. “The Department of Health may collect samples for the relevant cases again for further testing if necessary.”

Additional reporting by Gigi Choy