Police in north China's Hebei province have detained 22 people involved in a network connected with making and selling melamine, and tainting milk with the chemical.

Among the detained, 19 were managers at 17 pastures, breeding farms and milk purchasing stations. The local procuratorate has issued arrest warrants for 13 of them, according to the investigation panel of the Sanlu Group tainted milk case.

More than 800 police officers conducted raids on 41 pastures, farms and milk purchasing stations in Shijiazhuang, the provincial capital, and seized 222.5 kg of melamine.