FORT COLLINS, Colo. (NewsNation Now) — More strong winds made the biggest wildfire in Colorado history even worse, keeping firefighting aircraft on the ground and forcing evacuations along a highway leading to Rocky Mountain National Park.

Winds up to 70 mph and erratic fire behavior is expected throughout the day Saturday as the Cameron Peak Fire continues to expand.

People along U.S. 34 in the scenic Big Thompson Canyon — an area ravaged by flooding that washed the road out in 2013 — were in imminent danger and should get out immediately, Larimer County authorities said.

The growing fire has also forced firefighters north and east of Rocky Mountain National Park to reposition for safety.

“We are seeing very active fire behavior right now and firefighters are adjusting accordingly,” fire information officer Michelle Kelly said.

U.S. 34 was closed to non-emergency traffic, cutting off a major route to Estes Park, population 6,400, as well as the national park.

Firefighters focused on protecting homes in and around Drake and Glen Haven, an area with hundreds of cabins perched on heavily forested slopes and ridges. The wind, however, kept not only slurry-dumping airplanes from flying but aircraft that gave firefighters a view of the deteriorating situation from on high.

A voluntary evacuation zone extended as far as the Carter Lake area 8 miles west of Loveland for people who needed extra time and were advised not to wait for a dire emergency to leave.

The 173,000 acre fire set Colorado’s size record after strong winds Tuesday night and Wednesday morning caused it to grow by more than 25,600 acres. By Saturday morning 57% percent of the perimeter had been contained according to the Rocky Mountain Type 1 Incident Management Team.

It started in mid-August in the high country 30 miles west of Fort Collins and has persisted despite getting over 1 foot of snow on Labor Day.

The fire sent thick smoke into Fort Collins and prompted evacuations all the way to Horsetooth Reservoir on the city’s western edge. Partly because of the reservoir, the city of 168,000 wasn’t considered at risk, though schools for a time kept children indoors amid alerts for poor air quality.

The fire spread little during calm, cooler weather Thursday.

Twenty-five miles to the north of the Cameron Peak Fire, firefighters were also watching a windy forecast at the Mullen Fire on the Colorado-Wyoming line. The fire has grown little this week despite the recent wind.

Footage from near the Northern Colorado Regional Airport showed winds and smoke billowing from the mountains earlier this week.

The fires were unusually intense for October, when cold temperatures and snow have usually brought fire season to an end.

The Associated Press and NewsNation affiliate KDVR contributed to this report.