THORNTON, Colo. -

Fire crews are fighting a fire at a condo complex north of Denver.

The fire was burning in at least two three-story buildings in Thornton Tuesday.

A spokeswoman for the North Washington Fire Protection District, Sandy Danne, said one building has been damaged on all three floors, while the second has suffered less damage.

Helicopter video from KMGH-TV showed a large plume of smoke coming from the buildings, which are very close to others in the complex. The roof of one building collapsed.

No serious injuries have been reported. The cause hasn't been determined