SHANGHAI—Average housing prices in China fell in June for the first time in 16 months, official data issued Monday show, marking a long-awaited turnaround in the nation's overheated property market.

The nationwide index of urban residential property prices, which covers 70 cities, was down 0.1% in June from May, the National Bureau of Statistics said, marking the first such month-on-month decline since February 2009.

The...