HONOLULU (AP) — Two teenagers learning to fly were injured after their small airplane crashed on Oahu, authorities said.

The two 17-year-old girls were with a flight instructor on board the single-engine plane that crashed Monday evening shortly after takeoff from the Dillingham Airfield in Mokuleia, police said.

One girl hit her head, and the other, who was in the back seat, received some scratches. The teenagers were taken to a hospital in serious condition, Honolulu Emergency Medical Services spokeswoman Shayne Enright told the Honolulu Star-Advertiser. Instructor Victor Ponfiglio had minor injuries and refused medical treatment.

The 1969 Piper PA-28-140 owned by Alana Aviation crash in property adjacent to the airfield, police said.

The pilot was practicing "touch-and-goes" maneuvers, said Ian Gregor, Federal Aviation Administration spokesman. The FAA and the National Transportation Safety Board will investigate the crash.

Sonny Vaoifi was working on the property adjoining the airfield when the plane crashed. He said he saw the plane taking off and then it appeared to experience engine trouble.

"It started to sputter and had no power at all," Vaoifi said.

The plane turned right instead of ascending, he said. It made it over a chain-link fence before crashed into a plastic barrier and ending up in brush. He rushed over and saw the pilot and teens.

They were "shaken, with cuts and bruises, but they walked away," Vaoifi said.