Three youngsters were missing and 16 other people were injured after a fiery explosion that destroyed a remote mountain lodge as people started arriving for a family reunion, authorities said Sunday.

The three missing youngsters, ages 3, 12 and 15, were all from the same family, Delta County (search) Sheriff Fred McKee said.

"We are very concerned that they were last seen in the lodge," he said.

The explosion Saturday at the Electric Mountain Lodge (search) may have been caused by propane, which was used for heating, the sheriff said.

Authorities on Sunday afternoon called off the active search for the three. The charred rubble was still too hot for searchers to enter the lodge, and snow made it impossible to get heavy search equipment to the site.

The sheriff declined to say whether the youngsters were presumed dead. "This situation is certainly very grave," he said. "We have no one actively looking anywhere but at the scene."

The missing children were from the same extended family that owned the lodge, McKee said. Their names were not released.

Steve Douglas (search), one of the lodge's co-owners, was tending bar when he heard an explosion. He told The Grand Junction Daily Sentinel that he believed there was a gas leak under one of the adjacent condominiums.

Douglas' fiancee was on the third floor of the lodge when the explosion occurred. "She rode it down like an elevator," he said of the building's collapse. The couple both escaped without injury.

A family reunion was scheduled for the building. "Luckily, everyone hadn't arrived. It was pretty vacant at the time," Douglas said.

Because the lodge in the Gunnison National Forest on the western slopes of the Rockies is isolated by heavy snow, helicopters took injured people off the mountain while ground crews used tracked vehicles to ferry emergency medical teams to the site.

The lodge, about 230 miles southwest of Denver, has 12 rooms that sleep up to 34 people, according to its Web site. It also has three condos, but McKee said it was his understanding that the condos were still standing.

Injuries ranged from burns and smoke inhalation to "serious compound fractures," according to officials.