Shuttling through the Gongbei Border House every weekday has become a routine for Guan Hanlin, a hotel staff member in Macao.

The Macao resident lives with his wife and son in Zhuhai, a port city neighboring Macao that will return to China on December 20.

Guan's wife, Wang Liping, is an employee of a real estate company in Zhuhai. She said she does not see anything odd about marrying a Macao husband, in fact, she considers that they have similar cultural background.

Although separated by different administrations for hundreds of years, Zhuhai and Macao are as close as lips and teeth that they are called sister cities, and relations have been further cemented by cross-border marriages.

The two cities have recorded several thousands of cross-border marriage registrations and the number has been increasing by nearly a hundred every year, said Yang Huaigang, director of the marriage registration office in the Xiangzhou District in Zhuhai.

Jin Dan, a customs officer at Gongbei, told Xinhua that she can recognize many passengers, because they become familiar by going through the passageways twice a day, which takes less than two minutes. These people usually buy homes in Zhuhai and work in Macao.

Customs officials have seen an increasingly strong passenger flow, especially during China's traditional festivals, such as Spring Festival, Tomb-Sweeping Day, and Mid-Autumn Festival, which are shared by the people of both cities. The record number of those passing over from one side to the other in one day is more 100,000.