Three children have died and 35 people have become ill from drinking nitrite-tainted milk in China's north-western Gansu province, Xinhua news agency has reported in the latest food safety scandal to hit the dairy industry.
Most of the 35 were children under 14 now being treated at two hospitals in Pingliang city, Xinhua said, citing the local government and health bureau.
"An initial investigation shows all the patients were poisoned by nitrite after drinking bulk milk provided by two local dairy farms," Xinhua said.
Nitrite is used for curing meat.
The two farms were sealed off and their managers were being investigated, Xinhua said.
China's food sector has been beset by poisonings and toxin scandals that have shaken consumer confidence, and dairy production has been at the heart of those worries.
China's quality inspection agency last week ordered nearly half the country's dairy firms to halt production as part of a campaign to clean up the industry.
In 2008, at least six children died and nearly 300,000 fell ill from powdered milk laced with melamine, an industrial chemical added to low-quality or diluted milk to fool inspectors by giving misleadingly high readings for protein levels.
Earlier this year, Chinese quality authorities sought to calm renewed public alarm after reports that some manufacturers had illegally added a leather protein powder to dairy products to cheat protein-content checks.
Zhao Lianhai, who organised a website for parents of children who became ill from tainted milk after his own son became sick, was jailed for two-and-a-half years last November after being convicted of "inciting social disorder".