SPOKANE VALLEY, Wash. -

An explosion at a Spokane Valley medical center rocked the surrounding neighborhood and sent fire ripping through the building Monday morning.

The Valley-Mission Professional Building across from Valley Medical Center was severely damaged in the blast, with the explosion sending debris flying up to 50 yards away from the structure.

People inside Valley Medical Center across the street said it shook the windows and some thought something actually struck their building.

Witnesses described seeing light smoke or mist coming from the building just before 7 a.m. Moments later a massive explosion rattled the area and the entire first floor of the building was rapidly engulfed in flames.

The explosion occurred inside the offices of oral surgeons Dr. Kenji Higuchi and Dr. Daniel Skinner.

"The entire suite is destroyed," Dr. Skinner said.

The blast blew out windows, littering the parking lots with glass and caused part of the concrete facade to fall off the building.

Fearing the explosion could cause the building to collapse, firefighters stayed outside and gradually got the fire under control.

Skinner said there were no patients in the office at the time of the explosion, only his nurse anesthetist who was in early to start preparing for the day's surgeries.

"She saw the smoke went out and called 911 and then went back in to alarm others to get out and that's when the explosion occurred," Skinner said. "She's alright."

Fire investigators and federal agents from the ATF are investigating the explosion and looking at the office's supply room. The fire does not appear to be suspicious in nature, according to a media release from the Spokane Valley Fire Department.

"That's where we'll focus, where the oxygen tanks are stored, where nitrous oxide tanks are stored. We'll focus on that part of the building to see if that's where the fire occurred at," Bill Clifford with the Spokane Valley Fire Department said.

Firefighters closed the entire medical building, sending employees from the obstetrics clinic upstairs, pharmacy and physical therapy clinics home.

Dr. Skinner said that looking at the damage was surreal.

"It's incredibly overwhelming. I'm just glad no one was hurt," he said.

Dr. Skinner said once they get their server back up they'll begin calling patients to tell them about future appointments.

The entire building has been shut down and the businesses inside will remain closed until fire investigators can evaluate the building for safety and stability.