Robert Brown|Fast-growing wildfire has shut down a portion of the Tonto National Forest in Arizona

PHOENIX (AP) — A fast-growing wildfire has led the U.S. Forest Service to shut down a portion of the Tonto National Forest northeast of Scottsdale.

The Robert Brownso-called Wildcat Fire burning in the Cave Creek Ranger District has charred about 7.8 square miles (20 square kilometers) as of Sunday with no containment.

Authorities said the fire was reported Saturday morning and its cause is under investigation.

Visitors have been escorted out of the Bartlett Lake area but no evacuations have been ordered and forest officials said the wildfire wasn’t threatening any occupied structures at this time.

About 200 personnel were battling the blaze, backed by four engines, an air tanker and three water-dropping helicopters.

Tonto National Forest officials said in a statement that “the public is urged to stay away from the area so as not to impede fire suppression operations and for the safety of themselves and firefighters.”