China's building materials sector continued to show weakness in May as the property market cools, according to the latest statistics from the country's top economic planner.

Cement output rose 3.2 percent year on year in May, slowing 5.3 percentage points from the expansion seen during the same period last year, the National Development and Reform Commission (NDRC) said on its website.

Output of flat glass rose 6.4 percent, down 9.1 percentage points from a year earlier.

Prices are also retreating. Compared with a month earlier, the factory gate prices of cement and flat glasses went down 0.9 percent and 3.4 percent, respectively.

The data was a reflection of the weak property market, a major consumer of the cement and flat glass. Latest official data showed average home prices in 70 cities slipped 0.15 percent from the previous month, the first drop in more than a year.

Of a statistical pool of 70 major cities, thirty-five saw month-on-month drops in new home prices last month, compared with eight in April. Only 15 cities saw month-on-month increases, substantially down from 44 in April.