Grand Lake, CO – One person died and another was hospitalized in a structure fire and explosion early Sunday morning near Grand Lake, authorities said.

The Grand Lake Sheriff’s Office said on Facebook that deputies responded to a report of a structure fire at about 12:39 a.m., along with firefighters from the Grand Lake Fire Protection District and crews from the Grand County Emergency Medical Services, on Mad Moose Lane. The house “was a total loss,” it said.

One the home’s residents was outside when first responders arrived, was seriously injured and transported to the burn unit at Swedish Medical Center, said Grand County Sheriff’s Office spokesman Lt. Dan Mayer. He was later identified as Mark McLean, 63, of Grand Lake. McLean is in critical condition.

Another resident who could not be found initially was later located in the home and had died, Mayer said. She was later identified as Susan McLean, 66.

“Our condolences go out to the McLean family and entire Grand Lake community during this tragic time,” the sheriff’s office said on Facebook.

Crews extinguished the fire at about 9:30 a.m., he said, but the structure still has some hotspots, so crews will continue to monitor the scene.

The investigation into the cause of the fire and explosion is ongoing.

Mayer called the fire and explosion “pretty sizable,” and said it blew out walls of the house and items within about 200 feet of it.

He said officials don’t want to speculate on the cause, but because of its size, it could indicate something similar to a natural gas explosion. Although the house is in a residential neighborhood, no other homes or structures were threatened because of the distance between them, Mayer said.