Paris: Hurricane Leslie, the most powerful Atlantic storm to hit Europe in decades, has claimed at least six lives in France and left devastation in its wake as it also blew across Portugal and Spain, officials said on Monday.

Leslie dumped vast quantities of water across the west of the continent and left 28 people injured, including one in France, said Alain Thirion, prefect of France's Aude region. It was later downgraded to the category of a storm, Efe news reported.

"About 350 firefighters are in place, 350 more have been deployed," said French Prime Minister Edouard Philippe, adding that seven helicopters were mobilized to deal with the crisis.

Officials said that several months of rain fell in just a few hours overnight, blocking roads in some areas of France. One woman was swept away by the River Aude, according to local broadcaster BFMTV.

In one area, floodwater was as high as seven metres (23 feet). Authorities said that a warning for flooding was issued for the nearby French regions of Aveyron, la Haute-Garonne, Hérault, Pyrénées-Orientales and Tarn.

Leslie slammed into Portugal on Sunday and left a trail of destruction, injuring 27 persons. More than 100,000 homes were without electricity, flights were cancelled, hundreds of trees got uprooted and more than 60 persons evacuated.

By the time Leslie entered Spain it had reduced its speed to storm strength, but it deluged regions from Galicia to Tarragona with vast amounts of intense rainfall.

The Meteorological Service of Catalonia said it recorded very heavy precipitation in the regions of Blancafort, Prades, Falset, Ulldemolins and Torroja del Priorat.

Heavy rain and flooding affected the ancient walled city of Carcassonne on France's Mediterranean coast, where images showed a hospital submerged knee-deep in flood water.