CERVENY KAMEN, Slovakia - Two turbo-prop planes carrying civilian parachutists rehearsing for an air show collided in mid-air in Slovakia on Thursday, killing seven people, authorities said.

The dead were the four pilots and three of the parachutists, Interior Minister Robert Kalinak told reporters.

"Soon after takeoff, after the first manoeuvre, the two planes collided due to causes that are not yet known," he said. "All the people tried to save themselves, having parachutes on, and ... 31 managed to jump out without major injuries."

Of the 31 survivors, five suffered light injuries, a health ministry spokesman said.

Juraj Gyenes of Slovakia's Air and Naval Investigation Service told TA3 news channel the accident might have been caused by a possible overloading of one of the Czech-made L-410 planes that caused a sudden loss of altitude.

A Reuters photographer saw one of the planes in flames after it crashed into a forested hill near the village of Cerveny Kamen, 150 km (94 miles) north of the capital Bratislava.

The air show was cancelled, local media in the central European country said.