Police helicopters were searching Monday for a light aircraft that went missing with four people on board in southern France after its pilot ignored warnings and took off in stormy weather.

`The pilot took off while we were on orange alert because of the risk of storms and while meteorological conditions were awful, with heavy rain,` said Corinne Minot, a local official in the Drome area.

The single-engine Robin airplane took off on Sunday evening from the town of Romans in the Rhone valley and was heading south to Aix-en-Provence, near the Mediterranean coast, when it went missing.

Four police helicopters were concentrating their search in the south of the Drome department, where information from mobile phone operators pinpointed the passengers` cellphones, officials said.

Motorcycle police were also scouring the area for traces of the small plane.

Torrential rains on Sunday forced the evacuation of hundreds of homes in east-central France and cut two major highways.