ROCKY MOUNTAIN NATIONAL PARK, Colo. (AP) -- A wildfire that burned at least one cabin and forced the evacuation of several areas in and near Rocky Mountain National Park has grown to more than 3,500 acres.

The Fern Lake Fire grew rapidly Saturday morning, more than doubling in size before calmer winds allowed firefighters to gain the upper hand. The blaze, which was reported Oct. 9, is 20 percent contained.

About 1,100 evacuation and pre-evacuation notifications were sent to phones in the area Saturday, but officials say some people have been allowed to return home. The fire has so far been confined to the park, and the nearby resort town of Estes Park is largely unaffected.

Fire spokeswoman Traci Weaver says the blaze was likely caused by an illegal campfire.

No injuries have been reported.