On Chung Ying Street, the distance between Hong Kong and mainland China is literally a matter of crossing the road. Around 2,000 Hong Kong permanent residents live on the mainland side.

Access to the road from either Hong Kong or the mainland, however, is heavily limited. Only residents and workers who have permits can enter, while visitors need to apply for permission well in advance.

When Hong Kong officially closed all but three mainland border control points on February 8 – leaving only Shenzhen Bay, the Hong Kong-Zhuhai-Macau Bridge and the airport open – the Sha Tau Kok checkpoint, the border crossing for regular travellers closest to the town, was among those shut.

But at the northern end of Chung Ying Street sits another checkpoint, operated by the mainland government. Located just 400 metres east of the closed Sha Tau Kok checkpoint, the Kiu Tau checkpoint has never closed, according to residents and mainland officials.

And while Shenzhen authorities said after the Lunar New Year holiday that tourists could no longer go, an official from that city’s Chung Ying Street Affairs Office, who declined to be named, said residents had continued to come and go throughout the outbreak.

“We haven’t closed it because there are residents and workers who live there,” he said, adding that the Guangdong Province Security Bureau oversees the checkpoint.

Calls to the bureau have so far gone unanswered.

As of Monday, 418 confirmed coronavirus cases had been identified in Shenzhen, according to the city’s Municipal Health Commission. Hong Kong had 100 confirmed patients infected with the disease.

Speaking to the Post on Friday, one Hong Kong resident surnamed Lee, whose family lives on the mainland side of Chung Ying Street, said she was worried the open checkpoint and new exemption would increase the risk of an all-out viral outbreak.

“Of course we’re scared,” said the 23-year-old, who herself lives across the street in Sha Tau Kok, which counted just over 3,000 people as residents in 2016.

“It’s a huge loophole.”

That loophole, which leaves an apparent crack in the government’s mandatory quarantine defences, was spelt out on Thursday in a government press release that cited the border area’s “exceptional circumstances”.

The exemption criteria explain that Hong Kong residents living on the mainland side of Chung Ying Street can forgo compulsory quarantine “when entering Sha Tau Kok Frontier Closed Area (FCA) through Chung Ying Street” once an application has been approved.

Ko Wai-kei, whose constituency on North District Council includes the border area, defended the exemption as necessary for people who need to travel to Hong Kong.

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“I believe we have the flow of people in our control,” he said, adding that more than half of the 2,000 Hong Kong permanent residents living on the mainland side had applied for the exemption since the application process began last week.

Ko noted that anyone who travelled to Shenzhen or other parts of the mainland would still face a 14-day mandatory quarantine, though a copy of the application obtained by the Post includes no section for residents to list their travel history.

Lee, whose mother applied for the exemption for herself and her daughter, said no official asked about their travel histories.

Some medical experts questioned the decision to exempt residents travelling from the mainland amid the ongoing battle with the coronavirus, which causes the disease known as Covid-19.

The city should not make exemptions for anyone, regardless of where they live or proximity to the border, said Joseph Tsang Kay-yan, an infectious diseases expert.

“What are the scientific references and evidence to exempt this kind of people from the quarantine?” Tsang asked.

“As long as there are new cases happening in Shenzhen, the risks are still there.”

David Hui Shu-cheong, chairman of the department of medicine at Chinese University, said an exemption could be allowed if there was no outbreak in the nearby region.

“But these people need to guarantee they did not travel to other parts of China,” Hui said.

When the Hong Kong government announced a mandatory quarantine at the beginning of February, district councillor Ko wrote in a Facebook post that it would apply to residents living on the mainland side of Chung Ying Street.

At the time, people rushed back to the Hong Kong side of the border “like an animal stampede”, lugging necessities from vegetables to mattresses, recalled Lee, the 23-year-old resident.

But in the days that followed, no new measures came in.

On February 19, 11 days after the quarantine took effect, Ko reversed course, saying that quarantine would not apply to Chung Ying Street residents.

The uncertainty left a bad taste in some residents’ mouths.

Confused over what would happen and afraid of mingling with mainland residents, Kaylie Lee and her family moved out of Chung Ying Street to Sheung Shui right after the Lunar New Year holiday, as the virus outbreak worsened.

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She said she wished the government would close all checkpoints, including access to Chung Ying Street from Sha Tau Kok, even if existing quarantine measures seemed to be helping the situation.

“You don’t know who’s in Chung Ying Street, whether they’re mainland residents or not, so maybe [the quarantine] is necessary,” said the 23-year-old, adding that many residents had moved out on the same day.

One resident, 68-year-old Johnny Chow, who was raised on Chung Ying Street, said he believed few residents on the mainland side had taken advantage of the open checkpoint at Kiu Tau in recent days. Even if some had, he said, Hong Kong residents should not be punished with quarantine.

“Theoretically, the area they are living in has no infections,” he said, defending the exemption.

“How do you deal with people living here? They may need to go out to work, what should you do with that?”

Additional reporting by Zinnia Lee