Tempe Fire and hazmat crews are on-scene near Apache Boulevard and Rural Road, where dozens of people have been evacuated.
Tempe fire investigator Mike Reichling said it's happening at New School for the Arts and Academics, a charter academy.
"There were 45 people in the building at the time," he said. "They've all been evacuated. We're in the process of trying to find what the smell of the gas is being caused from. It could be a leak, a lot of times it could be sewer gas."
Reichling said no injuries have been reported.