Lam said it was only with the help of three mainland-linked laboratories – BGI, Kingmed and Hong Kong Molecular – that the city’s capacity to carry out the testing could be increased, and under no circumstances should Hongkongers doubt the sincerity of the central government.

“We need the public’s support, understanding and cooperation when we combat the outbreak … and the protection of the public’s health and safety is always our top priority,” Lam said.

“We understand the public may have different comments, but this time, it’s a matter of life. I hope society can value science and evidence, and stop all kinds of conspiracies, defaming, smearing and creating conflicts, and should not undermine the relationships between the central government and Hong Kong, especially as it was the [city] government that sought the mainland’s help this time.”

All residents could take a test if they wanted, with their identities represented by a bar code on specimen bottles and not revealed to the laboratories, Lam said. Only the Department of Health would know the identities of specific positive cases and this would address some privacy concerns in the community. The other samples would be destroyed in Hong Kong.

“If people still have concerns, they do not have to come forward. This is an entirely voluntary programme to provide testing for those who want to have a test,” she added.

The government’s decision to expand testing was down to the positive cases found during community tests carried out since last month, Lam said.

Samples taken from 137,000 residents in various high-risk clusters, including staff at care homes for the elderly, taxi drivers and restaurant workers, tested positive in 54 cases, according to Lam.

With that working out to one in about every 2,500 people, the government estimated there were at least 1,500 undetected cases in the community, suggesting the need for wider testing.

Other high-risk groups included workers in the catering, property management, transport, supermarket, postal and hotel sectors.

The government will also continue to conduct testing for such sectors, apart from the universal testing programme.

Lam noted the government would also work with Yan Chai Hospital next week to get all pregnant women tested and provided with documents proving their health status, which could then be used when they went for check-ups. The system was already in operation at care homes, she said.

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While short on details, Lam said testing could start in two weeks with social-distancing measures in place, and it would be made as convenient as possible for residents to pick up and return specimen bottles.

She also addressed concerns raised by some in the medical sector that the 60 mainland professionals tasked with helping on universal testing were exempt from having locally registered qualifications.

“Let me just stress that these personnel coming to help us to boost the testing capacity are not unqualified people,” she said.

“Please don’t misunderstand they are unqualified to do medical laboratory tests and we are making them qualified. No, they are qualified under the mainland system, but they want to operate in accordance with the Hong Kong legal system, so our law does provide for an exemption for certain categories of people.”

Lam said the mainland experts would carry out tests in a temporary lab to be built at Sun Yat Sen Memorial Park. They would be granted a two-month licence exemption under the city regulations governing medical laboratory technologists.

Lam said the government was not sure when six other experts who would help expand community treatment facilities would arrive.

“But even if they come, there’s no need for thousands of construction workers to come over, as our own ability can cope with that,” Lam added.

The expansion of makeshift facilities at AsiaWorld-Expo could be finished in weeks, while it would take a few months to build a temporary hospital at the site nearby.

Lam said Beijing attached great importance to the situation in Hong Kong and pledged to offer all necessary support at any time.

Professor David Hui Shu-cheong, a government adviser on the pandemic, said voluntary universal testing was the “second best” option, as mandatory citywide tests would not work without stay-at-home orders.

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“This is better than doing nothing, as Hongkongers would not be able to follow stay-at-home orders,” Hui said.

“The daily number of new cases remains at a high level, and there has been no significant drop yet. With the help of the others, testing more … can help isolate positive cases faster.”

Respiratory medicine specialist Dr Leung Chi-chiu said the main purpose of the universal testing was to reassure the public rather than cut transmission in community.

“As it is voluntary in nature, the testing can satisfy the public demands for testing. This is for assurance rather than controlling the epidemic,” he said.

But to utilise resources better, Leung suggested the three mainland labs should also help alleviate the workload of the Hospital Authority and the Department of Health.

Cheng Lai-king, chairwoman of the Central and Western District Council, said she was very disappointed with the government’s decision to set up a lab at Sun Yat-sen Memorial Park.

“The authorities did not consult the district beforehand. The park is near residential buildings, so residents are worried that the air discharged from the laboratory will contain viruses,” she said.