BEIJING - Following a recent series of collective food poisoning cases, particularly at schools, the Ministry of Health has issued a national alert over food safety problems.

Children receive treatment in a hospital in Shenxian county of Shandong province on Wednesday after 86 primary students suffered vomiting and diarrhea after eating lunch at their school. [Photo/ China Daily]

Summer and autumn are high seasons for food poisoning incidents and groups of people regularly eating at schools and construction sites are at particularly high risk, said the notice issued by the ministry on Wednesday.

In the past week, when the new school year started across the country, nearly 300 children were affected by problematic food or water provided at their schools in cases in Hebei and Jiangxi provinces, according to a report by Xinhua News Agency on Thursday. Most of the incidents occurred at primary and middle schools.

In the latest case on Wednesday, 86 primary students in Shandong province began showing symptoms of acute gastroenteritis after eating lunch at school, according to Xinhua.

By Thursday morning, 10 children were still under medical observation in a hospital in Shenxian county where they live, while others had been discharged, said a county government official.

Samples of the school's food were being examined and the government has ordered inspections for all school dining halls in the county, the official said.

In Longhua county, Hebei province, more than 130 students at the Zhangjiying Middle School fell ill after eating food provided by the school.

From Sunday, the students gradually began to show symptoms such as diarrhea and high fever, according to health authorities.

A father surnamed An, whose son goes to the school, said the teenager was still receiving treatment in hospital and did not feel like eating at all.

"But so far the hospital has failed to give any definite diagnosis and the school authorities have claimed the children might be suffering from an intestinal infection," An told China National Radio.

Experts with the area's disease control and prevention center said the children's illness was caused by norovirus, a virus that affects people's stomachs and intestines. They said the students got the virus from contaminated water.

To address these problems, the Ministry of Health ordered school canteens across the nation to improve hygiene and strengthen supervision of food safety.

In particular, the ministry asked the public to be wary of haricot beans, which are now hitting the market in large quantities.

"Canteens should boil them thoroughly because raw haricot beans make people sick," said the alert issued by the ministry.