Sodium nitrites were blamed in the food poisoning of the 74 students and four other teachers in a middle school in southwest China's Yunnan Province, local authorities said Tuesday.

The symptoms of dazzling and vomiting were discovered early Monday among the students and teachers in Wenshan First Middle School in Wenshan Zhuang and Miao Autonomous Prefecture in Yunnan, an official of the prefectural government said.

They were sent to the prefectural hospital and were in stable condition, the official said.

The cause of the food poisoning had been clarified after investigation found sodium nitrites in the glutinous rice made by a vendor outside the school, the official said.

The vendor's business had been closed, the official said.