The pilot was being checked out, and two other crew members were under observation after the crash at University of New Mexico Hospital in Albuquerque, authorities said. They didn't immediately release any names or the extent of the injuries but said none appeared to be serious. No patients were aboard the chopper.
Federal Aviation Administration investigators were at the hospital Wednesday night to begin an investigation, agency spokesman Lynn Lunsford said.
It wasn't immediately clear what caused the crash, but witnesses at the hospital said they felt a gust of wind at about 5:45 p.m. and saw the PHI Air Medical helicopter wobble as it started to take off from the helipad atop the six-story building. It came to rest on its side, and the damaged tail section could be seen hanging over the edge of the roof.
"They were taking off and had already dropped off their patient when it happened," said hospital spokesman Billy Sparks.
Images from TV news helicopters showed the roof around the wrecked chopper soaked as firefighters sprayed the tail section with water, but no flames were visible.
Jonathan Goss told the Albuquerque Journal he was in a dorm room and heard screeching. He looked out the window and saw black smoke pouring from the helicopter.
"In the movies, when a helicopter starts spinning out of control," said Goss, 20. "It sounded exactly like that."
Other witnesses said they saw a man rushing across the roof to the helicopter and sprinklers dousing it before firefighters arrived minutes later.
The hospital's fifth and sixth floors were evacuated as a precaution, Sparks said. Authorities were working to determine if there was any structural damage to the building.
It's unclear how long the hospital's helipad will be out of service, but Sparks said other hospitals have volunteered to help take incoming patients if necessary.
University and Albuquerque police closed roads around the hospital Wednesday night as the investigation on the rooftop continued. Inside the hospital's emergency operations center, officials were preparing for a briefing for first responders.
The crash at the hospital, in a busy area just north of the university, comes just weeks after a news helicopter crashed at an intersection near Seattle's Space Needle, killing both people on board. That crash prompted Seattle officials to review policies about permitting helipads.