BEIJING -- China's state reserves authority on Wednesday released a total of 150,000 tons of copper, aluminum, and zinc from the national reserves to alleviate burdens on businesses over rising raw material costs.

The National Food and Strategic Reserves Administration said it would step up monitoring of commodity prices and organize follow-up releases of national reserves.

This is the third batch of releases to the market. Previously, China has released a total of 270,000 tons of copper, aluminum, and zinc to maintain market order.

Since the beginning of this year, bulk commodity prices have surged due to factors including the overseas spreading of COVID-19 and the imbalances of supply and demand, causing pressures on medium and small firms.

Earlier official data showed China's producer price index (PPI), which measures costs for goods at the factory gate, expanded by 9 percent year-on-year in July, slightly higher than the 8.8 percent growth in June.

Sharp price hikes in crude oil and coal lifted year-on-year PPI growth in July. However, month-on-month data showed that government policies to stabilize commodity prices took effect, with mild price declines seen in industries like steel and non-ferrous metals, the National Bureau of Statistics said.