Flames roared unchecked through heavy timber for a third day in Montana's Glacier National Park, where the main road has been closed through the eastern half of the park, along with two campgrounds, during its busiest time of year.

The first major wildfire to hit Glacier in nearly a decade has charred roughly 4,000 acres (1,600 hectares) since igniting on Tuesday just east of the Continental Divide at Logan Pass, officials said, and has defied firefighters' attempts to contain it.

A group of hikers initially feared to have been in harm's way returned safely, and no injuries have been reported, though one historic log cabin was lost, the National Park Service said.