DENALI NATIONAL PARK AND PRESERVE, Alaska (AP) — Rescuers are trying 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 weren’t immediately known following the fall, which was reported to Denali National Park and Preserve rangers overnight, and rangers were seeking a weather window to allow them to reach the area by helicopter, a statement from the agency said. The four climbers were part of a seven-person team.

The three others climbing attended to those who fell, and then returned to camp, the statement says. The fall occurred near Denali Pass, at about 18,200 feet. The climbers returned to an area known as high camp around 17,000 feet, the statement says. McKinley stands at about 20,310 feet.

Over the years, many climbing injuries and deaths have occurred on the traverse between the high camp and Denali Pass, mainly resulting from unprotected falls.