Two 14-year-old boys and a pilot have been killed in a plane crash at a summer camp in Switzerland.

A third teenager - a 17-year-old girl - was badly injured in the crash.

Police said the single engine plane crashed into a mountainside during a summer camp flight for young aviation enthusiasts.

The four-seat Piper aircraft was on its second flight of the day and under the control of an experienced pilot when it crashed in the Diavolezza region around 10 minutes after take-off.

The cause of the accident is still under investigation.

The flight was organised for the camp for nearly 200 young people at the Aero-Club of Switzerland in the eastern area of Graubunden.

Camp director Yves Burkhardt said the sightseeing flight was supposed to be the highlight of the week-long camp.

"When I heard about the terrible accident this morning my world was shattered," he said.

 The camp had operated without any accidents for 35 years.