Hong Kong residents will be barred from quarantine-free travel to mainland China if a coronavirus infection is identified in their neighbourhood under the city’s new health code system, and it could take up to three weeks to be cleared for entry again, the Post has learned.

The health code will open for registration on Friday, and authorities are still working on the parameters of its “green”, “yellow” and “red” QR system.

It will be linked to the existing “Leave Home Safe” risk-exposure app, and while joining the new scheme is voluntary, anyone wanting to cross the border without undergoing isolation must use the new code. Only the green one will be accepted at crossing points.

Under proposals being considered by Hong Kong health authorities, participating residents living in the same building as a coronavirus patient would have their codes turn red, while those in the surrounding area would be assigned a yellow one due to the elevated risk of infection.

Once all residents in the designated area have taken a series of compulsory coronavirus tests – which could take as long as 19 days to complete after an infection is first discovered – their QR code will return to green if no more cases have been identified.

But just how large a geographical area the yellow code would cover had yet to be determined, a government source said.

“The delineation is a risk-based judgment, but it also has to be administratively operable,” the insider said. “Since there is no tracing function [on the ‘Leave Home Safe’ app], we have no choice but to be more liberal in delineating yellow.”

At this point, using the city’s geographical districts to define the yellow zones remained an option “under consideration”, the source said.

The scheme is likely to launch shortly after the December 19 Legislative Council election, according to insiders.

Danny Lau Tat-pong, honorary chairman of the Hong Kong Small and Medium Enterprises Association, said the red zone should be limited to the same residential floor where the infected person lived while the yellow zone should be restricted to the single building.

“The yellow zone should be as narrowly defined as possible,” he said. “If this zone covers a very broad district, then many uninfected residents will be implicated and barred from entering the mainland China for a period of time. This will defeat the purpose of the health code system.”

Lau argued that the yellow zone should extend no farther than 50 metres from the red zone.

Sze Lai-shan, deputy director of the Society for Community Organisation (SoCO), agreed, saying it defied logic if the yellow zone covered too large an area.

“If that is the case, it means a large number of people can’t use the health code for going to the mainland,” she said. “It doesn’t make sense at all.”

An extensive yellow zone was unnecessary as the number of infections in Hong Kong was low and most residents took sufficient preventive measures, Sze argued.

“All Hong Kong people are required to wear a mask outdoors,” she said. “Even family members who live with an infected person may not necessarily get infected. There is no need to broaden the yellow zone.”

Quarantine-free travel across the Hong Kong-Zhuhai-Macau Bridge will soon be taking place once more, though on a limited basis.

Hong Kong residents can start applying for the health code at www.healthcode.gov.hk from 9am on Friday. Users can also access the website through the updated version of the “Leave Home Safe” app (version 3.0).

They will have to export their visitation records from the risk-exposure app and upload them to the health code’s webpage. Once all the information has been uploaded, the data will be sent to relevant government departments and users will receive a coloured QR code.

Users will have to provide their full name and proof of home address for the health code, a feature that has triggered privacy concerns among some residents.

Once over the border, travellers must then use the mainland’s health code app, which tracks their whereabouts via mobile phone signal data from three major telecoms companies: China Telecom, China Unicom and China Mobile.

That app also shows which countries or cities a user has visited over a 14-day period.

People intending to travel beyond neighbouring Guangdong province must also have a valid mainland phone number and a WeChat account, as the mainland’s health code system is synchronised with the Tencent-backed app.

Hong Kong on Thursday also confirmed seven new Covid-19 cases, all imported, bringing the official tally to 12,478 with 213 related deaths. Fewer than 10 people tested preliminary-positive.

Air India was banned from operating flights between Delhi and Hong Kong till December 22, after arrival tests on Sunday detected an infection in a passenger, and another traveller did not comply with local health regulations.

Health authorities also announced that Estonia and Uganda would be classified as high-risk places from Sunday, with cases of the Omicron coronavirus variant detected in both countries.