Twenty-two pupils have fallen ill after eating at their school canteen Monday in southwest China's Yunnan Province, local authorities confirmed Tuesday.

The pupils, ranging from first to sixth graders at the Xiaoliuzhai Primary School in Hongdian Township of Wenshan City, experienced dizziness, nausea and vomiting around 11:40 a.m. after eating rice noodles for lunch and were sent to a nearby hospital, the Yunnan provincial emergency response office announced in a statement.

Health workers from the Wenshan Municipal Disease Control and Prevention Center had taken food samples for analysis and concluded that the food poisoning was caused by a highly toxic rat poison known as "Dushuqiang," the statement said.

To ensure that the pupils can get better treatment, local authorities transferred them to a hospital in Wenshan City, it said, without specifying their current condition.

The Xiaoliuzhai Primary School is a semi-boarding school with 150 pupils, with 71 pupils eating at the school for lunch Monday, the statement said.

Local authorities had also sent the other 49 pupils to the hospital in Wenshan City for medical observation, it said.

Local authorities are further investigating the cause of the food poisoning, it added.