By CBS3 Staff

CHESTER, Pa. (CBS) — Delaware County’s hazmat unit responded across the county following 25 separate reports of a gas odor, officials say. The reports began coming in around 10:30 a.m. Friday and were mostly in the western area of the county.

Some businesses closed early while Chester Charter Scholars Academy dismissed about 675 students after the school’s principal said some students and staff began getting sick because of the smell.

READ MORE: SEPTA Union Unanimously Approves Strike If Deal Isn't Reached

“It seemed to be affecting some of our students and staff who have asthma more intensely and for other people, they had burning sensations in their eyes,” Chester Charter Scholars Academy Head of School Akosua Watts said.

Corinne Canty rushed over to pick up her two sons, who are in the fourth and eighth grades.

“I smelled it when I came in. I smelled it when I was driving up here,” Canty said.

Officials don’t believe it’s an explosive gas and they’ve also ruled out a leaking pipeline. They still don’t know what it is, though.

READ MORE: Philadelphia Energy Solutions Refinery Rebranded As The Bellwether District

“We never detected any levels that were high enough to cause an explosion or fire anywhere in the county,” Delaware County Emergency Services Director Tim Boyce said. “The product was so dispersed you could smell it, but you could never detect the product.”

No injuries were reported but some people reported headaches, officials say.

“If you’ve ever tried to turn the stove on and you leave it on and smelled the gas, that’s exactly how it smelled,” a Delaware County woman said.

The cause of the smell has not been determined at this time, but the Department of Emergency Services is working with state and local refineries to locate the source of the odor.

MORE NEWS: Philadelphia Weather: Chance Of Severe Weather As Parts Of Region Could See Up To 3 Inches Of Rain

CBS3’s Chantee Lans contributed to this report.