Hong Kong's decision to implement "ambush-style" lockdowns in neighborhoods to contain the coronavirus pandemic has left some residents trapped inside shops, sometimes overnight.

In one recent operation, a 10-year-old girl was in a hair salon getting a trim when her mother left to buy food when the order was issued. Eventually, authorities allowed the daughter to reunite with the parent after taking down the girl's personal details.

The strategy of closing off areas, often overnight, while residents are tested one by one has been criticized by some health experts. While one suggested an overhaul of the approach, another warned residents should not leave home late at night.

Authorities locked down 17 blocks in Sham Shui Po on Tuesday night but after screening residents, they failed to uncover any cases. One photo from the operation that went viral showed a customer of a hair salon at 263B Ki Lung Street lining up to be tested with his hair still wrapped with plastic, the dye job only halfway done. The owner, a man surnamed Chan in his 30s, said the customer was "angry" over the sudden lockdown.

"He managed to go home and wash his hair in the end. He will come back and resume his hair cut after work later," Chan said.

Two other customers were also stuck in the salon with him and had to produce a negative Covid-19 test result before authorities allowed them to leave by late evening.

Chan's part-time employees had left before the operation began. But he had to stay the night and could only open his business after 10am when police officers removed the barrier tape.

"It was inconvenient," he said. "But we had to cooperate with the government. If they let you go then you go, otherwise you just have to stay here."

When authorities locked down Majestic House in Tsim Sha Tsui on Monday night, about 30 people became trapped in the Hair Peace salon. Again, no new cases were uncovered during the operation.

"Our staff, guests or people in the entire building are safe," the business said in a Facebook post on Tuesday. "For all the guests who stayed in our store last night, we are very sorry for the hard night."

The 10-year-old girl was among them and was only finally able to reunite with her mother at around 11pm.

"After the Home Affairs Department became aware of the situation, the girl was tested and had her information registered, then she was allowed to leave with her mother at our discretion," a department representative said.

Authorities did not directly reply to inquiries about how they might handle such situations where residents were locked inside a business differently or whether they would alter their strategy to prevent it from happening again.

At least seven of the 10 lockdown operations conducted since January 23 have failed to identify a single new infection. The government said the lack of any new cases from recent operations was "expected", as the aim was to screen residents before transmission chains could form.

But respiratory expert Dr Leung Chi-chiu called on the government to re-examine existing lockdown measures as they had brought "unnecessary risk" to people, noting the number of local cases had been decreasing.

"Even if we find a few cases out of a few thousand, it's just a very small number," Leung said. "It's not logical to detain customers in shops and buildings ... These individuals are unnecessarily exposed to further risk (by being stuck together). They should be released right after testing to reduce the chance of exposure."

Leung suggested the government take down the information of customers or other people caught up in the operation and release them. If they developed symptoms, the details could still be used to track them down, he added.

But infectious disease expert Dr Joseph Tsang Kay-yan disagreed, saying the lockdowns were "within expectations" and there was little the government could do to make such measures more convenient for the community.

"They believe they have to do it to make sure the number of cases can be brought down as soon as possible," Tsang said. "I would advise the public not to stay out after 7pm ... and not to go to areas previously set up to do compulsory testing."

Despite the hassle, some people affected by the Sham Shui Po operation remained supportive.

Chan Cheuk-ming, the owner of restaurant Pei Ho Counterparts, backed the strategy despite being trapped on his premises.

"It's good to lock down so all asymptomatic carriers can be identified," Chan said. "I got tested and it went smoothly. Maybe it's because they allocated time slots according to buildings."

He added: "After a lot of (negative) comments during the three-day lockdown in Yau Ma Tei, they immediately fixed it and only locked down specific buildings to be done in one day, so there's less inconvenience."

A man surnamed Lai, 64, slept at the guest house where he is employed and simply began working again in the morning.

"Of course it's a little troublesome to be stuck, but there's no choice as this is mandated by the government," he said. "I will return to work otherwise there will be no business for my boss, and I will feel bad."

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