Whipped up by strong winds, the blaze took hold around 3:30 pm (local time) and has spread over 2,260 hectares (5,600 acres) of scrubland, grass and some wooded areas, according to firefighters.
"We haven't seen a situation like this for a very long time," the fire service said, first calling the wildfires "out of control" but later describing more favourable conditions in the night.
Homes were destroyed in the town of Vitrolles, some 30 kilometres (20 miles) north of Marseille, with more than 1,000 people forced to seek shelter in local sports centres.
The blaze - which comes after low rainfall in winter and spring left southeast France extremely dry - sent a huge pall of smoke into the sky over the port city of Marseille.
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"The fire seems to be less intense than before but is not yet under control," Marseille mayor Jean-Claude Gaudin said in a tweet.
Further west in Herault, four firefighters were injured battling another blaze when their vehicle was surrounded by the flames.
Road and air transport were badly affected by the fire yesterday evening, with two motorways closed and some flights cancelled at Marseille airport.