Chief Executive Carrie Lam Cheng Yuet-ngor said people with cross-border needs to visit families, attend funerals and go on business trips will be given priority in the initial phase of border reopening. But cross-border students will not be given priority in the first stage as that involves many people.

She said boundary crossers must be fully vaccinated, test negative for Covid-19, upload their LeaveHomeSafe records to the Hong Kong government server and use the mainland health code upon crossing land boundaries.

In an interview with the Hong Kong Economic Times published on Monday, Lam said the initial phase of border reopening will likely be restricted to Guangdong province and citizens will be able to head north via land ports with Shenzhen or to Zhuhai through the Hong Kong-Zhuhai-Macao Bridge.

But travelers will need to have a mainland mobile phone number so mainland authorities can trace them upon being identified as a confirmed case or close contact.

Local authorities last Tuesday had an online meeting with mainland experts from the National Health Commission to further discuss details of the quarantine-free travel scheme.

Sources said mainland officials intend to establish a circuit-breaking system for the quarantine-free travel scheme with Hong Kong to suspend travel upon just one unknown-source infection, although SAR authorities are negotiating for a threshold of at least two cases. It is also said that the quota will be set at 1,000 a day.

Sources said a mainland delegation likely to be led by top expert Zhong Nanshan may arrive in Hong Kong at the end of this month at the earliest to inspect and advise on anti-pandemic controls, paving way for the scheme next month.

Infectious disease expert Ho Pak-leung from the University of Hong Kong said it is reasonable if the mainland wants to suspend the scheme with one untraceable source infection in Hong Kong.

"Hong Kong is not capable of doing lockdowns involving an entire district. Unless authorities can quickly identify sources of infections for each case, it's reasonable for the mainland to set the threshold at one case in the initial phase, which is the same for the mainland-Macau scheme," he said.

The president of the Chinese Manufacturers' Association of Hong Kong, Allen Shi Lop-tak, urged authorities to reopen borders with the mainland in January, so Hong Kong businessmen could visit their factories before the Lunar New Year in early February, typically a peak season for them.

He said Guangdong has more than 20,000 SAR-owned enterprises and called for authorities to allow a daily quota of between 1,000 and 2,000.

Hong Kong recorded zero Covid-19 cases on Monday, with five preliminary imported cases pending confirmation. The last time the SAR saw no cases for a day was on October 10.