At least 7 dead in helicopter crash

(CNN) - At least seven people were dead and three more critically injured Sunday after a midair crash between two medical helicopters at a hospital in Arizona, authorities said.

The collision, at Flagstaff Medical Center in Flagstaff, Arizona, set fire to a 10-acre area, according to fire officials.

The crash happened at roughly 4 p.m., said Capt. Mark Johnson of the city's fire department.

"As you can imagine, we've got lots of heaps of metal to go through," Johnson said. "It's just difficult right now."

He said there is a landing pad on the roof of the hospital that is used by medical helicopters.