() Approximately 30 children were rushed to the hospital on Friday with a mystery illness that also led to the evacuation of two school buildings.

First responders raced to Mapleton High School in Ashland, Ohio, at around 10:20 a.m. local time after dozens of children suddenly got sick by an unknown substance.

Children at Mapleton Middle School complained of headaches, nausea, and dizziness, local affiliate WJW reported. Some of them said they felt shaky and 30 children were taken to hospitals.

The schools were evacuated as first responders investigated. They ruled out a gas leak and it’s unclear what caused the students to get sick.

“Out of an abundance of caution, both Mapleton Middle School and Mapleton High School were evacuated to ensure the safety of all students and staff,” Mapleton School Superintendent Scott Smith wrote in a letter to students and staff.

The children were said to be doing well after being taken to the hospital as the investigation into what made them sick continues.