Rescuers are working to reach four climbers who fell on Alaska's Mount McKinley, North America's tallest peak, the National Park Service said Thursday.

The climbers' conditions were not immediately known following the fall, which was reported to Denali National Park and Preserve rangers overnight. Rangers were seeking a weather window to allow them to reach the area by helicopter, according to a park service statement.

The four climbers were part of a seven-person team. The three other team members attended to those who fell before returning to camp at 17,000 feet. The fall occurred near Denali Pass at approximately 18,200 feet on the mountain, which stands at 20,310 feet.

The park service said weather conditions on the mountain were improving and would soon enable helicopter operations. The agency did not immediately respond to requests for additional comment.

In a separate incident on Wednesday, two climbers were evacuated from the mountain by helicopter around 11 p.m., though the park service did not provide additional details about that rescue.

The typical climbing season for Mount McKinley begins in late April and continues into mid-July. It was not immediately clear how many climbers are currently on the mountain.