Updated

A small civilian helicopter crashed Friday just south of Black Canyon City, killing two people, officials said.

Sheriff's spokesman Doug Matteson said that no others were on board the helicopter, which crashed just off of Interstate 17 about 35 miles north of Phoenix.

The cause of is unknown. FAA spokesman Ian Gregor said his agency will investigate the crash, but had no further details.

Destiny Najera, a 22-year-old Prescott Valley resident, told the Prescott Daily Courier that she was driving on Interstate 17 toward Phoenix when she saw a small helicopter rise in the air just yards from the highway.

"All of a sudden the propellers just stopped and things started falling off," Najera said. "Then it fell and burst into flames. A big, black puff of smoke kind of covered the whole area. It was crazy."