A person in dark clothing was seen running away from a St. Clements business moments after an explosion and fire, police say.

Fire broke out around 12:30 a.m. Thursday at The Fitness Edge on Lobsinger Line, northwest of Waterloo.

At the time, Mark Koenig was awake inside his nearby pet store.

Koenig says he heard a noise loud enough to pierce through his headphones, and went outside to investigate.

“I looked down toward the fitness place, and I (saw) somebody running across the road,” he told CTV News.

That prompted Koenig to walk over to the fitness studio, where he saw flames and broken glass.

He called 911, and grabbed dirt from a nearby planter to extinguish a small part of the fire.

Moments later, the first fire truck showed up.”

“Upon arrival, our crews noticed smoke (coming) from the building,” said Wellesley Township fire chief Andrew Lillico.

Matt Gibson, who owns The Fitness Edge, was contacted next.

Thursday afternoon, he expressed astonishment at the morning’s events.

“It’s totally shocking. It’s unbelievable,” he said.

“I don’t understand the ‘why’ behind it.”

While the fire was quickly extinguished and no injuries were reported, firefighters stayed at the scene for several hours to ensure its safety.

“The building has significant structural damage,” Lillico said.

The fire is being treated as suspicious. The Office of the Fire Marshal has been called in to investigate.

Koenig calls it “disheartening” to realize a suspicious fire could have been set in his community.

“In a small town, we should be sheltered from things like this,” he said.

Gym members can access the facility around the clock by entering security codes. It’s not clear if that’s what happened early Thursday morning.

Police say anyone with information about the fire should call them or Crime Stoppers.