An economics professor on Monday said the reopening of the border with the mainland should push retail sales up by 50 percent in the coming year.

High-speed trains between Hong Kong and the mainland resumed on Sunday after a three-year break, while quarantine-free travel with the mainland resumed on January 8.

Hong Kong-based, Kevin Tsui, from Clemson University in South Carolina, said it would take more than a year for the sector to fully recover.

"For the whole year, I think that is going to help more than 50 percent. The airline industry claimed that within a year, they can get 70 percent of the capacity resumed. From that perspective, the retail sector can do a little bit more than that," he told RTHK's Hong Kong Today programme.

Meanwhile, retail and wholesale sector lawmaker Peter Shiu said most travellers from the mainland came to visit their relatives or had business purposes, but he expects more tourists later, which would further boost the SAR's retail sales.

"High-speed trains brought us many tourists [before the pandemic]... Those tourists have a relatively high purchasing power, so resuming high-speed rail service is a huge step toward returning to normalcy," Shiu said.

"Retailers said there were more people near West Kowloon station. There's a 20 to 30 percent increase in the number of customers for luxury stores, such as jewellery shops, in Tsim Sha Tsui."

The lawmaker added that the situation in Sheung Shui is different as many retail stores had closed down, but he believes businesses will return soon as well.

Up to 60,000 mainland travellers are allowed to enter Hong Kong every day, while an extra 15,000 people a day will be able to enter Hong Kong at land crossings in the four days leading up to Lunar New Year.

Shiu said the government should speed up the process and allow more travellers to the SAR as soon as possible.