Officers investigating the deaths of six primary school students in Shanxi have detained the school's three staff members and are not ruling out the possibility the children's food was deliberately poisoned. The children, aged from six to 11, were among 11 students boarding at a school in Nanyao village and were sent to the Puxian County People's Hospital for treatment on Monday night, an hour after they were found in comas in their dormitories. The two boys and four girls had eaten dinner in the school canteen and were pronounced dead on arrival at the hospital. Police detained the school teacher, cook and a boiler operator and cordoned off food stalls in three nearby villages. Samples had been taken from the school canteen and the stalls for testing, the Shanxi Business News reported. Last night, Puxian party secretary Yang Zhiping told Xinhua that preliminary investigations had ruled out natural food poisoning as the cause of death, but it was believed the six students had ingested the same poisonous substance. Police were still investigating, but did not believe the substance was rat poison or pesticide. The incident follows a spate of food scares in recent weeks, including reports of tainted Hebei duck eggs, turbot treated with banned antibiotics and bean curd sheets that may contain cancer-causing chemicals. A Puxian county propaganda official said yesterday local authorities were seriously concerned. 'This tragedy is a big event in our region. Relatives of the children have been asked to stay in the government's hotel and cadres are trying to calm them and ease their grief,' the official said. The children came from five families, with one couple losing both their 10-year-old daughter and six-year-old son. Some distressed parents were admitted to hospital.