YINCHUAN, June 9 (Xinhua) -- Police in northwest China's Ningxia Hui Autonomous Region have detained 23 people suspected of making and selling drugs, and seized more than 4.5 tonnes of drug-making raw materials, local authorities said Saturday.

Police in Wuzhong city in November received reports about a gang installing equipment for producing hydroxylamine, a raw material used in drug making.

A four-month investigation led to a drug production and sales ring operating in six Chinese provinces and regions, according to Wuzhong police.

Twelve of the 23 suspects have been prosecuted and the case is under further investigation.