Breckenridge, CO – An explosion leveled a winter sports building on Saturday, temporarily trapping a man and leaving a dog missing.

Witnesses say they think the explosion was caused by ignited propane or natural gas inside the main office of Good Times Adventures, located at 6061 Tiger Road, however the official cause is not yet known.

Good Times Adventures is a snowmobiling and dog sledding business. All of the dogs, except for one, have been accounted for. Their conditions were not immediately known.

Vacationer Tim Schlis was nearby when the building exploded. He says he looked at his watch and saw it was 11:20 a.m. Right after that, he was pushed forward by a massive explosion. He turned around and saw what he says was the biggest explosion and cloud he’s ever seen.

“There was a cloud going up 800 feet, 1,000 feet in the air,” said Schlis. “Big hunks of plywood just flying through the air and we thought somebody had dynamited something till we started seeing insulation fly everywhere.”

Schlis says he and his friends went up toward the site of the explosion.

Another car came down the hill and the person inside said they were going to call 911 because they couldn’t get cell phone service.

“We went up there to see if anyone was there,” said Schlis. “But we smelled natural gas so we just backed off and I went down to call 911 as well.”

Schlis says when he went up near the blast, there was debris everywhere. Branches that had been blown off nearby trees were lying everywhere, he says.

According to Schlis, it took authorities about 30 minutes to respond. One man was located inside the rubble, buried up to his chest. Authorities were able to dig him out around 3:45 p.m. He was conscious and alert at the time. He was airlifted to Denver by a Flight for Life helicopter. The Summit Daily News has identified him as Brian Mislanski.He’s listed in critical condition at St. Anthony’s Central.

A spokesperson for the Red, White & Blue Fire District says the building that exploded was the main office, with an apartment upstairs.

“There was a Good Times building up there and we drove there early this morning. It was all intact, and it’s gone. I mean, just totally gone. It’s just spread all over the woods,” said Schlis.

Other nearby buildings remain intact.

Crews from Lake Dillon Fire-Rescue, the Summit County Sheriff’s Office and Summit County Ambulance also responded.