At least 13 people died as flash floods struck southwestern France on Monday after torrential overnight rain, reported Reuters. One person is reported to be missing. “The toll risks going up,” an unidentified Interior Ministry spokesperson was quoted as saying.

National emergency services spokesperson Michael Bernier confirmed the fatalities, which took place in the southern district of Aude. Officials said that thousands were being evacuated from the area after the equivalent of seven months of rainfall happened in just six hours. Several roads were cut off due to the overflowing river.

Seven helicopters were deployed to rescue people, said the prefect of Aude, Alain Thirion. “We have people stranded on rooftops,” said Thirion. “We are going to have to use aircraft to evacuate them because we cannot reach them by boat given the force of the water.”

The floods are the worst to have hit the Aude river in more than 100 years, reported the BBC, quoting French weather monitoring service Vigicrues.

Prime Minister Edouard Philippe, who visited the disaster zone, said 700 emergency service workers have been deployed to help out in the rescue operations.

Around 1,000 people were evacuated in the area of Pezens, located near Carcassonne in Aude area, amid fears that a nearby dam could burst, AFP reported. Carcassonne, a fortress city, has been swamped by the flood waters.