HONG KONG—Residential property transactions in this Chinese city fell sharply over the weekend after the Hong Kong government slapped a 15% tax on property purchases made by foreigners, part of fresh measures aimed at curbing speculation in an overheating market.

Hong Kong Financial Secretary John Tsang said Friday the new measures show the government's resolve to stabilize the residential market while the easy lending environment continues to boost demand for property, despite an economic slowdown.

"This...