MONTROSE, Colo. (KDVR) — Four people were injured in an explosion at the Hartman Brothers building on Wednesday.

The explosion happened at around 3 p.m. at the building located at East Main Street and North First Street.

The Montrose Fire Protection District said the building was fully engulfed in flames when crews arrived on scene.

Four people were hospitalized following the explosion. Two are in good condition, one person is listed as in fair condition, another person is in critical condition.

“We lost a building, but we saved a block,” said Montrose Fire Protection District Chief Tad Rowan. “I am proud of the quick work of our responders in immediately providing protection to the other flammable gases on site. This plan of attack limited the damage to the structure and the area. Our hearts go out to the individuals impacted by today’s incident, and to our community for the fire damage to a historic downtown building. I am grateful to our local and regional agencies that assisted with today’s response.”

While fighting the fire, MFPD said crews had to take additional precautions because there was bottled oxygen and other flammable gasses present at the building.

The cause of the explosion is under investigation.