Some 700 firefighters backed by water-dropping aircraft struggled to control fires that earlier consumed 1,500 hectares (3,700 acres) of brush around La Motte, 20 kilometers (12 miles) from the coast in the Var department, with two new outbreaks reported during the day.

Emergency workers said they had evacuated 1,000 holidaymakers from a campsite near La Motte, not far from the town of Draguignan.

And 17 firefighters were injured -- two seriously -- as they fought a blaze near Salon-de-Provence, in the Bouches-du-Rhone department to the west. A huge cloud of smoke stretched nearly to the port city of Marseille, some 30 kilometers away.

Fuelled by a heat wave and the worst drought in a quarter of a century, the fast-moving forest fires have ravaged parts of southern France and Corsica since Monday, leaving five people dead, including four foreign tourists.

Greece and Norway offered water-dropping aircraft to French emergency services on Wednesday, following in the footsteps of Italy and Russia. For the first time, Paris has been forced to call in foreign reinforcements.

Police and officials along the popular Riviera coast said the simultaneous eruption of several fires on Monday indicated criminal gangs could be at work, and they pointed to three Molotov cocktails found near one of the fires.

"Twenty-nine fires breaking out almost simultaneously in the Var (on Monday), including seven in Frejus... I don't think that there can be any doubt about the theory of criminal intent," Frejus mayor Elie Brun told AFP.

The government has promised to act without mercy against anyone found responsible for starting fires, with Justice Minister Dominique Perben warning that arsonists who kill can face life in prison. Identity checks were introduced in high-risk areas.

But some officials warned against assuming the fires were of criminal origin, saying the vast majority were likely to have been started by human negligence or natural combustion due to the hot, dry weather.

"The myth of the evil arsonist must not become a permanent alibi that lets everyone else off the hook," said Bernard Foucault, who is in charge of forest protection on the Mediterranean coast. "The person who most often starts a fire is Mr or Mrs Everyman."

According to the interior ministry in Paris, 25 separate fires were reported overnight Tuesday on a 400-kilometer (250-mile) stretch from the Alps to the Pyrenees -- a number it described as "highly surprising."

"This number does not even include the smaller fires of less than a hectare which also require manpower to put out," said Eric Souprat, spokesman for the civil security service.

Firefighters managed to control the fires that broke out Monday in the Maures hills nearer the shore, which killed two Britons, a Dutch woman and a Polish man. A fifth victim died on the French island of Corsica.

But with forecasters predicting more hot weather and a Mistral wind of up to 80 kilometres (50 miles) an hour, emergency services remained at the ready.

Some villages remained without electricity on Wednesday as power lines were switched off to allow water-dropping planes to operate safely.

The destruction caused by the fires has raised questions about the region's development. In recent decades, highly inflammable woodlands have replaced farmers' terraces and pastures, while rapid population increase has led to large numbers of new houses being built on the edge of the forest.

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TERRA.WIRE