A deadly rat poison known as dushuqiang has been blamed for the food poisoning that affected 53 students in the city of Sanhe, in North China's Hebei Province, on Thursday, according to the local health agency.

Twenty-three students are still in hospital in a stable condition, according to the local hospital. The rest have been allowed to go home.

"We're almost certain that this is a criminal case and the poison was put in the food deliberately," a director of the information department of the local municipality told China Daily yesterday. "Public security officials are still trying to discover who could be responsible."

Students said they started twitching and vomiting after having dinner at the No 2 dinning room of Sanhe No 2 Middle School at about 6 pm. Most of the students who showed symptoms were sent to the nearby Yanjiao People's Hospital. Eighteen who were in a critical condition were sent to the 263 Hospital in Beijing's Tongzhou District early the following morning.

"I had some porridge and a steamed stuffed bun for dinner, but after a few minutes I felt like throwing up," said a grade-one student who suffered from the poisoning but did not want to reveal her name. "We were served porridge, rice, steamed stuffed buns and some stir-fried dishes that evening."

The information department director said most of those who were poisoned were senior-one students who had just returned from military training. "The time for students to have dinner varied from grade to grade. It happened that senior-one students were having dinner at the No 2 dinning room at that time," he said.

Tests carried out on the vomit revealed rat poison, a kind that attacks the nervous system.

The poison, which was made with a substance called tetramine, has been banned since 1991, but is still widely available in the countryside because no other effective rat poison is available. There is no effective antidote.

(China Daily September 26, 2005)