Austrian leader Sebastian Kurz says his thoughts are with the friends and families of two top climbers missing in Canada along with an American.

The Austrian chancellor on Friday described David Lama und Hansjörg Auer as "two of the best-known and best extreme climbers ... of our country."

Lama, Auer and American climber Jess Roskelley have been missing in Alberta's Banff National Park since Wednesday and are presumed dead after an avalanche.

Kurz said Lama and Auer had "shaped the international climbing and alpinist scene in recent years with many achievements."

Lama, the son of a Nepalese mountain guide and an Austrian woman, was feted for achieving the first free ascent of the Compressor Route of the Cerro Torre, one of the most striking peaks in the Andes.