Over 20 teachers and students were treated for injuries after a possible chemical spill at an Indiana high school on Tuesday, local officials said.

According to the Indianapolis Fire Department, 12 staff members and nine students at Beech Grove High School experienced throat irritation after a mysterious white, hazy cloud filled a girls’ bathroom, Fox 59 reported.

Within minutes the entire school — about 1,000 students — was evacuated, school officials said.

Firefighters searched the bathroom but found no evidence of a chemical spill on any surfaces.

Authorities remain uncertain about what may have caused the bathroom haze, according to the news outlet. No meter readings were found during their search.

“At this time, we really have no idea what was deployed inside the bathroom,” IFD Battalion Chief Rita Reith told Fox 59.

Fire officials described all of the injuries as “slight” — with all 21 students and staff reporting that they had an itch and raspy feeling in their throats. They were all treated at the scene and none were taken to the hospital.

Beech Grove High School students were taken to a nearby community center and elementary school before they were bused home. After-school activities were all canceled.

The school will be thoroughly cleaned overnight, and classes are expected to resume tomorrow.

School officials said they would be reviewing security camera footage to investigate what may have occurred.

“A disruption of the school day like what was experienced today is unacceptable, and we will work tirelessly to ensure that the cause of the incident is uncovered and appropriate consequences are rendered,” Beech Grove Superintendent Dr. Laura Hammack said in a statement.