Two Germans have been arrested on suspicion of running an illegal campsite in southern France after it was hit by flash floods, leaving one man missing.

Two senior officials of a German youth organisation that ran summer camps for children and young people were being questioned by police on Friday after it was alleged that the campsite had no official approval. The Planjole site in Saint-Julien-de-Peyrolas, about 30 miles north-west of Avignon, is located in an area prone to flooding, local officials said.

The pair remained in custody on Friday, facing possible charges of "causing injury and endangering lives, working illegally and running a campsite without permission,” said Eric Maurel, the Nimes public prosecutor.

About 1,600 people, mostly campers, were rescued by helicopter on Thursday night as the authorities ordered the evacuation of several sites in the Gard, Ardèche and Drôme areas.

Some 10 people were treated in hospitals for minor injuries or hypothermia. Empty caravans and cars were swept away by the floodwaters. Some were smashed into trees.