SHANGHAI stocks edged down today as small-cap stocks declined after data showed manufacturing activity at private firms shrank for the first time in seven months, overshadowing the property sector's gain.

The benchmark Shanghai Composite Index declined for a third straight trading day, falling 1.34 points, or 0.06 percent, to 2,299.25.

HSBC's China Purchasing Managers' Index, a gauge of manufacturing activity slanted more towards private and export-oriented firms, fell in May to 49.2, down from 50.4 in April, HSBC Holdings PLC announced today.

It was the lowest level since October 2012 and the first time in seven months the index fell below 50. A reading of 50 or higher indicates activity is expanding.

"The falling index indicated that small and medium-sized enterprises, which contribute the most to employment, are still facing difficulties," Qu Hongbin, HSBC China's chief economist.

The environmental sector declined the most. Beijing Capital Co, a company engaged in water treatment, dropped 3.6 percent to 8.07 yuan. Tianjin Capital Environmental Protection Group Co lost 2.3 percent to 9.17 yuan.

Most property developers gained after data from the China Index Academy today showed average home prices in China's 100 major cities gained 0.81 percent in May, its 12th straight monthly increase.

The average price rose 6.9 percent year on year, 1.56 percentage points higher than the pace of April.

Poly Real Estate, China's second largest developer, added 0.9 percent to 12.35 yuan. Gemdale Corp increased 1.5 percent to 7.87 yuan.