"The six must have eaten some poisonous substance at the same time, and they all died shortly afterwards," Yang Zhiping, the Communist Party secretary of Puxian County, Linfen, in Shanxi Province, was cited by the Guangzhou-based Nanfang Daily as saying yesterday.

The four girls and two boys were students at a primary boarding school in Nanyao Village, Puxian County.

They said they were feeling sick around 8:30 pm on Monday and then died before being sent to hospital at 9:40 pm.

Because they became ill after supper it was first thought they had died of food poisoning.

The five other students at the tiny school of just 11 students were transferred to a nearby school.

Police are still investigating the case.

Linfin Vice-Mayor Miao Yuanli rushed to Puxian on Monday night to address the situation.

Local police along with educational, health and epidemic prevention authorities as well as officials from the food and drug administration are all investigating the incident, said Miao.

The parents of the six children were said to be devastated by the loss and are being looked after at a hospital.

The provincial education bureau has ordered schools to step up food safety inspections and increase awareness of health issues among students and staff at school canteens.

It also ordered schools to ban canteen staff from entering food-processing and storage rooms.

"The tragic event has set off alarm bells in our schools, and we must learn a lesson from it," said Yang.