About 760,000 mainlanders have settled in Hong Kong through the one-way permit scheme since the handover in 1997, making up more than one in 10 residents.
And there is no plan to stop or change the scheme, which allows 150 mainlanders a day to reunite with their families, since it is in line with mainland law, a top Security Bureau official says.
The issue of new arrivals was raised in the Legislative Council yesterday amid concerns about how government policy met their needs and whether a review of the system was in order.
About half of the migrants came to live with their spouses and half reunited with their parents, while a small number relocated to be with their children, acting secretary for security John Lee Ka-chiu told lawmakers.
"New arrivals on the strength of one-way permits are among the important sources of population growth in Hong Kong."
The Immigration and Home Affairs departments collected the statistics through records of new arrivals at the Lo Wu checkpoint and data from the Registration of Persons Offices, Lee said.
The information goes into a quarterly report that is sent to relevant departments. The Census and Statistics Department, for instance, would take new arrivals into account when making population estimates that in turn helped the government in its long-term planning for education, housing, transport, social services and health care, Lee said. "The administration will consider relevant issues when formulating population policy," he said.
Dr Chung Kim-wah, assistant professor in Polytechnic University's department of applied social sciences, criticised the government for responding too slowly to the new migrants' housing and medical needs.
"I have encountered many cases where women of mainland origin, together with their children, saw their public housing applications rejected after their husbands died or they divorced."
Chung, however, acknowledged the difficulty in further easing the eligibility for flats, given the limited new housing on hand.
Democratic Party lawmaker Sin Chung-kai suggested asking the mainland authorities to review the system, including handing over to Hong Kong the work of vetting, approving and issuing one-way permits.
Lee said there were no "justifications or need" to change the scheme or approval arrangements, or to add more screening criteria. "The policy objective … is to allow mainland residents to come to Hong Kong for family reunion in an orderly manner … in accordance with the laws and regulations of the mainland."
Mainlanders can also gain residency rights via the Quality Migrant Admission Scheme - which targets highly qualified people who lack a prior job offer - or Capital Investment Entrant Scheme, which requires investment of at least HK$10 million.
Correction: an earlier version of the story carried an erroneous headline. It was corrected at 10am March 21.