A paediatrician on Saturday urged parents planning family trips to the mainland to ensure that children are vaccinated against Covid-19.

Ahead of the return of quarantine-free travel on Sunday, Dr Mike Kwan from the University of Hong Kong said only a quarter of children aged between six months and three had received the jab.

“It's worrying because half of the children aged between six months and three have never been exposed to Covid-19. They have never been vaccinated or infected. If they contract the virus, they might develop serious complications or die in unfortunate cases,” he said.

“If parents plan to take their kids to the mainland after the border is reopened, they should let them receive the shots as soon as possible."

He noted that some parents are concerned about the side effects of the vaccine, but he said the jabs have been proven to be safe.

He also advised people travelling across the border to keep their masks on and practise good hygiene.

An initial quota of 50,000 Hong Kong residents per day will be able to go to the mainland without serving quarantine from Sunday, while about 10,000 more will be able to travel by air, ferry or take a bus across the bridge to Macau and Zhuhai.

The same number of places will be available for mainland residents to come to the SAR.

Hong Kong officials said on Friday that 340,000 bookings had been made in an online system in the 24 hours after its launch on Thursday.