BELVIDERE, N.C.- The North Carolina Highway Patrol says four people have been killed in the crash of a medical helicopter.

Patrol spokesman Master Trooper Christopher Knox said the Duke Life Flight helicopter went down around 11:45 a.m. Friday near the town of Belvidere, close to the Virginia border and about 160 miles east of Raleigh.

Knox said it's not known where the helicopter was headed when it went down and authorities have no idea what caused the crash. He said the Federal Aviation Administration has been notified and state troopers are on the scene to secure the site.

The Duke Life Flight web page says its helicopters usually have two critical care providers and a pilot onboard and can only carry one patient at a time.