National emergency services spokesman Michael Bernier said 13 people had been killed and one person was still missing.
Seven helicopters were scrambled to rescue people from the roofs of their homes, and rough weather was making operations hard.
"We have people stranded on rooftops".
Six helicopters were scrambled to help rescue people from the roofs of their homes, but bad weather was making operations hard, the prefect of Aude, Alain Thirion, told BFM TV.
Flash floods have left several people dead in southwest France, with roads swept away and streams become raging torrents as the equivalent of several months of rain fell overnight, authorities said Monday.
At least six people died after heavy storms swamped parts of southwestern France, flooding rivers and cutting roads, officials said Monday. Some 350 firefighters were involved in rescue operations, a number which will double as more are drafted in to deal with the aftermath. We're going to have to use aircraft to evacuate them because we can not reach them by boat given the force of the water.
A nun was swept to her death by rising waters in the village of Villardonnel, where her convent was partially destroyed, and at least four died overnight in Villegailhenc, local authorities said.
The French weather service, Meteo France, issued a warning of flood risk for all surrounding departments for 24 hours.
A spell of torrential rain resulted, with Carcassonne recording 70mm of rain in just three hours. The Aude region is a popular tourist destination with old towns and villages in its hilly peaks and land stretching down to the Mediterranean.
Several residents told local media that the situation sharply deteriorated around 3 a.m., forcing people to scramble to higher ground as they sought safety.
The Aude river reached levels not seen in more than 100 years, the French agency responsible for monitoring, Vigicrues, said.