(CNN) -- At least seven people died and three were critically injured Sunday when two medical helicopters collided in midair near a hospital in Flagstaff, Arizona, authorities said.

At least one person killed in the crash was a patient, according to FAA communications manager Ian Gregor.

The patient and two others were aboard a Bell 407 helicopter operated by Air Methods Corp., an air medical service provider, Gregor said. No further information about the other victims was immediately available.

The skies in Flagstaff were clear Sunday afternoon, CNN meteorologist Karen Maginnis said.

The helicopters crashed around 3:45 p.m. in a wooded area near a neighborhood, Flagstaff Police Department Sgt. Tom Boughner said.

No one on the ground was injured or killed in the crash, but two rescue workers were injured by an explosion after the crash, Boughner said.

The collision ignited a 10-acre brush fire that was soon contained, according to fire officials.