Juneau, Alaska — A fall near Denali Pass on Mount McKinley left four climbers in uncertain condition, prompting a rescue response from the National Park Service, the agency said Thursday.

The accident was reported to Denali National Park and Preserve rangers overnight. The Park Service did not immediately release the climbers’ conditions or identities. Rescuers were positioned to reach the site at about 18,200 feet on North America’s highest peak — which rises to approximately 20,310 feet — but were delayed by weather that limited helicopter access.

The four climbers were part of a seven-person expedition. The three uninjured members attended to their companions after the fall and then made their way back to the high camp around 17,000 feet, according to the Park Service statement. No further details about the cause of the fall or the climbers’ nationalities were provided.

Rescue operations on the mountain, commonly known as Denali, can be treacherous due to extreme altitude, rapidly shifting weather, and the technical difficulty of Denali Pass, a narrow corridor near the summit. The Park Service said it would attempt to reach the fallen climbers as soon as conditions allowed.