Hong Kong can consider easing social-distancing measures enacted to limit the spread of Covid-19 but should begin testing all arrivals twice – once after entering Hong Kong and again at the end of their mandatory two weeks’ self-isolation, health experts say.

Double-checking would help catch any infected people who were asymptomatic and before they began moving around the city, they said.

The call came as Hong Kong recorded its third day of zero new coronavirus cases this past week, leaving the tally at 1,037, with four related deaths.

Secretary for Food and Health Professor Sophia Chan Siu-chee repeated the government’s warning that despite the encouraging dip, it was essential the city remained aggressive in its fight against the pandemic.

“Even though there are signs that the outbreak in Hong Kong has eased, the global situation is still severe and unstable,” Chan wrote on her blog on Sunday. “I hope society will not lower its guard or else the results from our measures will be for nothing.”

Pressure has been mounting on the Hong Kong government to relax coronavirus travel restrictions between the city and mainland China, with some politicians calling for an exemption for business travellers.

Health authorities have stressed the disease can only be considered under control if the city goes at least one or two incubation periods without recording new cases, or about two weeks to a month.

Dr Joseph Tsang Kay-yan, an infectious diseases expert, said Hong Kong had become relatively safe and the crux of the challenge was keeping it that way. Some visitors had developed symptoms during their 14-day home quarantine and failed to alert the government, he noted.

“Most of the infections now are imported cases,” Tsang said. “It’s not enough that visitors are only tested once when they arrive in Hong Kong. They need to be tested again by the end of their mandatory quarantine.”

Since Monday last week, air travellers have been tested twice, once when they entered Hong Kong and again near the end of their home quarantine. Those arriving through the Hong Kong-Zhuhai-Macau Bridge, and the Shenzhen Bay Port, who have not visited Hubei province in the previous 14 days, do not need to be tested.

All non-residents have been banned from entering, except travellers from Macau, Taiwan and mainland China who have not been to any foreign country in the last 14 days. All airport arrivals are immediately tested and must wait for the results before beginning self-isolation. On Friday, 1,315 people entered the city and another 932 on Saturday, most of them locals.

But the government is gearing up to bring back 5,200 residents stranded throughout India and Pakistan on chartered flights. Tsang said they should be evacuated in groups to ensure facilities in Hong Kong were not overloaded and sent directly to quarantine centres.

To control the spread of the disease, the government has shut 11 types of venue, including bars, pubs, gyms and beauty salons, until at least May 7, although a rule requiring restaurants operate at half capacity was lifted last Friday.

Dr Leung Chi-chiu, chairman of the Hong Kong Medical Association’s advisory committee of communicable diseases, said authorities could begin lifting some social-distancing measures, but curbs for high-risk communities, such as homes for the elderly, must remain in place.

“With earlier cases, we could see that the main transmission sources were places where people would take off their masks. Those should remain under control,” Leung said, referring to bars and karaoke lounges. “However, I think we can start allowing civil servants to go back to work or for the Hospital Authority to resume its non-emergency services.”

Leung also warned against lifting border restrictions too quickly and agreed with Tsang’s suggestion of a second test on visitors.

“Testing twice is a good idea,” he said. “But I think the government should requisition suitable hotels and just isolate travellers there, so their movements can be monitored throughout the quarantine period and they can be tested before they are released.”

Leung also called for wider testing within communities to ensure asymptomatic carriers were identified and isolated. “As long as we can get the infection sources under control, locally there is not much we need to worry about,” he said

Civic Party lawmaker Kwok Ka-ki, a urologist, said that while the city could consider relaxing some social-distancing measures, it must not ease any restrictions on visitors because the contagion was still a serious threat in many countries.