Police in central China's Henan Province ruled out intentional poisoning Friday after a preliminary investigation into Thursday's campus food poisoning incident that left dozens of students sick.

"We are yet to pinpoint the cause of the incident, but there's no evidence of intentional poisoning," the public security bureau in the provincial capital Zhengzhou said in a press release.

Dozens of students at Henan University of Technology in Zhengzhou complained of stomachaches, diarrhea and vomiting Wednesday night. By 2 a.m. Thursday, the school clinic sent 27 serious cases to a nearby hospital.

All the patients were in stable condition Friday.

The city's disease control and prevention center carried out lab work on samples of food taken from the canteen Thursday, but the test results have not been made public.

The university has blamed the accident on a company that was in charge of logistic services on the campus. The company's food and beverage manager and a chef of the canteen were suspended from work to answer questions from the police and generally assist with the investigation.

The canteen was closed for an overhaul.