The environmental group Green Sense said on Tuesday that the government's search for housing land will be endless if it doesn't cut the number of immigrants from the mainland.
Green Sense said its study found that more than 110 hectares of land have been rezoned for flats in the past five years.
The group's Roy Tam said in that same period, some 300,000 mainlanders came to Hong Kong through one-way permits, the quality migrants scheme and a study scheme.
This, the group says, adds to the housing pressure in Hong Kong.
Green Sense said the 110 hectares of rezoned housing land are about the size of six Victoria Parks. It said the sites used to be community halls or other government facilities, greenbelt land or open space.
Tam said these were valuable buffer sites that had a cooling effect among the territory's high-rise buildings.
He said if the government is willing to cut the number of mainland immigrants by half, there would be some 200,000 fewer people living in Hong Kong in 2024. That Tam said, would ease a lot of housing pressure.
Tam also urged the government to provide an immigrant-control scenario when its new land supply task force discusses ways to solve Hong Kong's housing woes.