A Slovak military plane crashed into a snowy mountain in Hungary late on Thursday after starting its descent too early, killing 42 people, mostly peacekeepers from a Nato mission in Kosovo.

The only survivor phoned his wife to raise the alarm just after the plane crashed in mid-evening and was in a stable condition in a hospital in Kosice, Slovakia.

Hungarian officials said initially the plane had diverted from its correct flight path, but later clarified their statement to say it was about three kilometres off the ideal trajectory, but still within the permitted corridor.

A Slovak official said visibility was very good and the experienced pilot, whose plane had been serviced regularly, had not reported any technical failure.

"The pilot flew along the set flight path. The only problem was that he started descending too early,"

Slovak Air Force commander Juraj Baranek told a news conference.

Difficult terrain and freezing temperatures hampered efforts to reach the crash site, 700 metres up in a forested, uninhabited mountain area, Hungarian officials said. The plane was 20 kilometres from its destination, Kosice air base.