Dozens of students from multiple primary and middle schools in northwest China's Qinghai Province have been affected by food poisoning, local authorities said Wednesday.

As of 3 p.m., more than 20 students from three schools in Hui-Tu Autonomous County of Datong had been sent to a local hospital for treatment, sources with the county government said. Their conditions have not yet been disclosed.

The students showed symptoms of food poisoning such as vomiting and diarrhea after eating lunch at their schools, according to the sources.

An investigation into the cause of the accident is under way.