The odor was reported after 9:00 a.m. Thursday on the second floor of the facility on South Wrangleboro Road.
Intial reports indicated the odor was coming from a second floor storage closet that houses various chemicals and supplies.
The entire school, including some 1900 students, was evacuated to a nearby football field. A HAZMAT condition was declared, and ambulances were seen going in and out of the area all morning long.
Parents, some of whom gathered at the entrance to school property hoping to find out what was happening, got some calls from students who had been evacuated.
There was also a mass calling to parents from the school district, but it didn't provide many details.
"My son texted me, he said he's okay," one mother told Action News. "I told him to call me, but he couldn't call. So I don't know how he's doing or what's happening."'
"I don't know if they have their phones on them," said another mother, Linda Meuer. "It's possible they were just evacuated and they didn't grab anything. I'm very worried."
Action News received word around noon that students were being allowed back in the building.
The police car that was blocking off the entrance to the high school left just before noon. And what appeared to be most of the HAZMAT units were also seen leaving.
Parents were told that some students were affected by the fumes, but it was not clear what symptoms they were treated for, or if they were treated at the scene or somewhere else.
The nature and source of the fumes was still unclear.