WARREN, Mich. -- About 900 students were safely evacuated Wednesday from Lincoln High School in Warren after a fire broke out, school officials said.

Principal Pat Victor said the roof and exterior walls of the school’s gymnasium, which is under construction, caught fire.

“A couple of welders were welding and a hot cinder hit this yellow material that’s a vapor barrier, and it’s extremely flammable,” Victor said. “The welder had his fire extinguisher are his side and he dispensed the remainder of the fire extinguisher, but that didn’t satisfy the fire and we called 911.”

Victor said there were only about 150 students inside the school at the time of the fire because of ACT Testing.

Classes were canceled for the rest of the day.

Victor said the interior of the school was not damaged and that classes will resume Thursday.