The fire at the camp outside the port city of Dunkirk destroyed wooden shelters, and came hours after a clash involving up to 150 migrants, the prefecture of the region said.
Riot police moved into the camp to break up the trouble that one migrant said pitted Afghans against Kurds.
Five people were injured in the fight among 100 to 150 migrants, leaving three of them in hospital with knife wounds, the prefecture said.
Officials linked the fight with the fire that broke out hours later but stressed that an investigation is needed to determine its cause.
No injuries were immediately reported because of the blaze.
Firefighters worked to contain the flames lapping the night sky and devouring the fragile shelters of migrants who were evacuated to local gymnasiums. The prefect, the highest state official in the region, rushed to the scene.
“I lost all my documents,” said an Iraqi migrant who identified himself only as Albidani, standing outside the camp. “I just have only this paper that says I'm a refugee in France.”
He said Kurds and Afghans had clashed before the fire erupted, but he did not know why.
“We are refugees here in France. We don't have any place... we don't know what to do. We lost everything,” Albidani said.
Up to 1,500 migrants were living in the over-populated camp, the prefecture estimated,
The camp in the Dunkirk suburb of Grande-Synthe was set up a year ago by Doctors Without Borders.
The neat rows of wooden shelters replaced a squalid makeshift tent camp nearby rife with traffickers preying on migrants.
Humanitarian groups said the original camp was filthier and more dangerous than a huge makeshift camp in Calais, about 19 miles to the west, that was dismantled by the state in October.
The population of the new Dunkirk camp swelled after the one in Calais was torn down.
Clashes, as well as small fires, have occurred in the past in the La Liniere camp. French officials decided last month that the camp population must be reduced to 700 and security increased to keep out traffickers.
The authorities said the camp must be dismantled bit by bit with migrants housed in special centres, like the thousands of migrants evacuated from the Calais camp.
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