Two small aircraft, one towing a glider, collided in mid-air near the Boulder, Colo., airport Saturday, killing five people, authorities said.

Four of the people killed were on a Cirrus plane that had clipped the tow cable behind another plane pulling the glider, WUSA-TV, Denver, reported.

One person in the tow plane was also killed.

The glider released from the towline and landed safely.

Both planes crashed in an uninhabited area over two sites separated by a ridge and debris covered several miles, authorities said.

Amateur video showed one aircraft with a parachute attached falling to the ground. Witnesses also reported fires on the ground.

Hugh Walton of Boulder, who lives a half mile from the crash site, took the video.

"I realized this is a plane with a person in it and I thought, 'Oh, that is not good,'" Walton said. "I glanced over my shoulder and I saw some smoke and some flames going on way up in the sky."