Around 500 people have been forced to flee their homes since yesterday as flames fanned by strong winds consumed more than 3,000 hectares of mainly scrubland and forest and gutted several homes.
French President Francois Hollande said authorities believe some of the fires were started deliberately and vowed that the perpetrators would be tracked down.
The Portuguese holiday island of Madeira was also counting the cost after three people were killed by fires.
Wildfires in Madeira's picturesque capital Funchal, which had turned the sky orange and forced foreign holidaymakers to be evacuated, were brought under control overnight.
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In the Marseille suburb of Pennes-Mirabeau, one resident was too scared to return to her home after a harrowing night.
"It was terrible, there were flames in front of the house, at the side and behind," said the woman, who asked to be identified only as Martine.
At the port of Fos-sur-Mer, northwest of Marseille, 800 ha. Went up in flames on Wednesday and caused fears for the safety of oil and chemical terminals.
Transport by road and air was badly affected by the fire yesterday, with two motorways closed and some flights cancelled at Marseille airport.
Fire service Lieutenant-Colonel Nicolas Faure said 1,200 firefighters were still working to dampen down smouldering areas of brush and trees, but said he believed the danger was subsiding.
"The situation is improving," he said.
Police arrested a man Wednesday near the town of Vitrolles on suspicion of starting one of the fires deliberately.
Hollande, speaking in his home region of Correze in central France, said "those responsible will be found and punished".