OTTAWA — Three professional mountain climbers were missing and presumed dead on Thursday after an avalanche in Banff National Park in the western province of Alberta.

The three were identified as Jess Roskelley, an accomplished American mountaineer, and David Lama and Hansjörg Auer, both Austrian, by the North Face clothing company, their sponsor.

When the men failed to return from their climb as scheduled on Wednesday, Parks Canada, the government agency responsible for the park, said that it immediately sent aircraft to search for them. The aerial survey found, the agency said, “signs of multiple avalanches and debris containing climbing equipment” in the area where the three had been climbing.

“They are missing and local search and rescue has assumed the worst,” the North Face said in an email. “We are waiting to learn additional information as the search mission continues.”