Fifteen people who were poisoned after drinking tainted milk on Thursday was released from hospital Saturday, local authorities said.

A nurse at the Pingliang Hospital in Pingliang city, Northwest China's Gansu province, puts an intravenous drip into a toddler who is suffering from food poisoning, on Friday. [Photo/Xinhua]

A total of 39 people were sent to local hospitals in Pingliang City of northwest China's Gansu Province Thursday after drinking nitrite-tainted milk. Three children younger than two years old were killed. The youngest was 36 days old.

Fourteen people were discharged from hospital Saturday, while another one was discharged Friday, according to a statement from the Pingliang municipal government.

It said most of the poisoned were children under fourteen. One of them remained in serious conditions.

An initial investigation shows all the patients were poisoned after drinking milk provided by two local dairy farms. Further investigation is under way.