A government pandemic advisor, David Hui, said on Sunday the government may need to lower the cross-border travel quota, if public hospitals see a surge in Covid-19 patients.

After the resumption of quarantine-free travel to and from the mainland on Sunday, medical experts like Hui expect more people in Hong Kong to come down with the coronavirus in the coming days.

The Chinese University professor said this is in part because there are no vaccination requirements for mainland arrivals, unlike travellers from other places.

But he stressed after attending a television programme that Hong Kong has a good immunity barrier because of its high vaccination rate and the fact that many people in the SAR have already been infected.

The scholar said Covid is now endemic worldwide, and the key is whether the mainland border reopening would create a major burden for local public hospitals.

"If the local healthcare system can cope, then you don't need to tighten restrictions again," Hui told reporters.

"But if many arrivals are serious Covid patients, they take up the beds in local hospitals, then you have to tighten again - such as lowering the quota, increasing PCR testing or even adopting a vaccine mandate for mainland arrivals."

As the government plans to allow cross-border students to attend schools in Hong Kong after the Lunar New Year, Hui said it's a bit of a concern that the vaccination rate for young children is still at less than 15 percent.

He said officials should consider scrapping the outdoor mask mandate this summer, but mask-wearing should continue to be enforced on public transport and at indoor areas.

However, Hui said at some point isolation orders for Covid patients should also be dropped for those with mild or no symptoms.

Macau announced on Saturday that as Covid is becoming endemic there, patients with mild symptoms can go to work.