BEIJING, June 9 -- China's producer price index (PPI), which measures costs for goods at the factory gate, went down 3.3 percent year on year in May, the National Bureau of Statistics (NBS) said Monday.

On a month-on-month basis, the PPI dropped 0.4 percent in May, according to the NBS data.

NBS statistician Dong Lijuan attributed the decline of PPI to falling international crude prices, which drove down domestic prices in petroleum-related industries, as well as a seasonal slowdown in demand for energy and raw materials, with coal prices easing and construction activity disrupted by hot and rainy weather in southern regions.

In May, the purchasing prices for industrial producers dropped by 3.6 percent year on year, the NBS data showed.

China's consumer price index, a main gauge of inflation, was down 0.1 percent year on year in May.