TOULOUSE, France (Reuters) - A French judge placed two German nationals accused of operating an unlicensed holiday camp in southern France under formal investigation after a flash-flood swept through the site, leaving several children injured and one man missing.

A local prosecutor on Saturday said the two men faced charges of unintentionally causing injuries and putting lives in danger, as well as establishing a campsite without authorisation.

Rescuers evacuated more than 180 people from the site in Saint-Julien-de-Peyrolas, north of Avignon, after torrential rain on Thursday transformed the Ardeche river into a raging torrent of muddy water.

Divers have not found a 66-year-old holidaymaker who sought refuge from the swollen river in his caravan, only to be swept away.

Lawyers for the two men could not be reached for comment. They were already facing legal proceedings filed by the local authorities for breaching planning regulations.

"We're confident that the camp site was located in a flood zone and that the town hall had alerted the owners of this and the danger that represented," said Eric Maurel, the Nimes prosecutor.

"On the very day of the incident, the town hall again signalled the immediate danger and they still did not clear the site, unlike other nearby campsites," the prosecutor added.

Under France's legal system, a suspect is not formally charged with a crime unless sent to trial. Saturday's move by the judge puts the two men a step closer to that.

(Reporting by Johanna Decorse; Writing by Richard Lough; Editing by Andrew Bolton)