Updated

More firefighters are on their way to a fire that has burned across more than 11 square miles in northern Colorado and is approaching a reservoir for the city of Greeley.

U.S. Forest Service officials say the blaze about 20 miles northwest of Fort Collins grew from about 1.5 square miles to more than 11 square miles Thursday amid erratic winds. The fire is approaching the city of Greeley's Milton Seaman Reservoir, but city officials say the water supply hasn't been affected yet.

About 15 homes remain evacuated, down from 80 earlier Thursday, but residents have been told to be ready to leave again if conditions change.

Some 400 firefighters are on the scene, and more are expected to arrive Friday.

The fire is among several burning around the West.