A trio of skiers is likely buried under an avalanche near Anchorage, Alaska, that occurred Tuesday afternoon, but dangerous backcountry conditions have so far stymied recovery operations, officials announced.

Alaska State Troopers say three skiers who had flown by helicopter to a remote mountain range were swept away by an avalanche and likely killed under the weight of snow nearly as deep as a 10-story building.

The group was traveling with guides from a commercial heli-skiing operation, which escorts backcountry skiers via helicopter to the tops of mountains that are otherwise inaccessible.