An explosion that destroyed a longtime rock and jewelry shop in downtown Eustis Thursday morning is under investigation after a natural gas leak and utility work preceded the blast, Fire Chief Michael Swanson said during an afternoon press conference.

The explosion occurred at 10:57 a.m., roughly an hour after firefighters first responded to a reported gas leak caused by nearby road and utility construction. Swanson said crews arrived around 9:30 a.m. and discovered a leaking natural gas line.

“There was some road work being done and utility work being done, and we discovered a gas leak, a natural gas line,” he says.

Utility crews from TECO People’s Gas crimped and contained the leaking line before the explosion occurred. Swanson emphasized that while the leak was outside, investigators are still working to determine how the blast happened.

“From what I understand, the ensuing event occurred after the line was crimped,” he says. “We’re trying to determine what caused the explosion and the fire.”

One woman who was inside the building at the time suffered serious injuries and was flown from the scene. Her name or how she was associated with the business was not released.

“It was pretty bad, so I would venture to say critical,” Swanson says, adding that he had not yet received an official medical update.

The shop was described as a longtime and well-known business dealing in jewelry, rocks and gemstones.

“At this time, the building appears to be a total loss,” Swanson said. He noted that the explosion “looks like it took place in the back of the building.”

The cause remains unclear. Swanson said investigators face a challenge because the structure did not appear to have active gas service.

“The building actually doesn’t have gas service to it that we know of,” he says. “Everything in the building is electric, and we’re not finding any gas that also remains on the building.”

However, the business used soldering and welding equipment in the back room, which investigators will examine.

The State Fire Marshal, the gas company’s investigator and Eustis Police are all on scene.

Swanson says firefighters evacuated all four corners surrounding the business after gas migrated into utility lines underground, something he described as common.

Among the cleared buildings were Water Customer Services, Ace Hardware and a nearby facility that serves people experiencing homelessness.

“I sided on the side of caution and I made the call to get everybody to leave,” he says.

No gas was detected inside those structures. The only gas reading came from the home directly behind the business, where firefighters measured 10 percent gas concentration on the second floor, likely from gas rising through eaves and windows.

All evacuees were later allowed to return.

Swanson confirmed firefighters were still on scene when the building exploded.

“We had evacuated and told people to move,” he says. “We had people relocate their cars. We did all of our part.”

The fire escalated quickly from what began as a routine gas leak call.

“When they run those fiber optic lines down, it’s not uncommon for them to hit a gas line,” Swanson said. “This one was outside. Everything was going according to plan, and that’s when the explosion occurred.”

Multiple agencies responded, including departments from Mount Dora, Tavares, Umatilla and Lake County. Swanson thanked them for their help.

“We have such a great relationship and such a great response package for Lake County as a whole, and it really served its purpose today,” he says.

The area will stay closed while the scene is treated as a crime scene for investigative purposes.

Swanson acknowledged the emotional impact on his department and the city.

“It’s a local business,” he says. “We’re a small town in America. This is a great place. Everybody’s friends. We all take care of each other. I don’t like it when my friends in my city get hurt.”

As for what might have happened had firefighters not already evacuated the area, Swanson said it could have been a lot worse.

“If this explosion would have occurred and we didn’t evacuate and close the road, obviously, there could have been multiple people in the building,” he says. “The evacuations worked.”

The investigation will continue to find a cause for the explosion.