DENVER (AP) — Nearly a dozen helicopters will fill the air as Denver-area emergency crews practice for a mass disaster.

The exercise Wednesday is a major test of the National Disaster Medical System. It will involve more than 200 simulated patients, 11 metro-area hospitals, 10 ambulances and 10 helicopters. Part of the exercise will involve Denver International Airport.

The program is designed to coordinate medical care in national or international emergencies.