About a dozen people were injured in the blaze, according to local officials.
“There is nothing left but a heap of ashes,” Michel Lalande, the prefect of France’s Nord region, told reporters at the scene.
More than a thousand migrants, mostly Iraqis and Kurds, had lived in the camp in some 300 closely packed wooden huts.
According to Lalande, “it will be impossible to put the huts back where they were before.”
The prefect explained that the migrants had been evacuated and rehoused in gymnasiums that had been converted into temporary emergency shelter in the Dunkirk suburb of Grande-Synthe.
Local official Olivier Caramelle affirmed the extent of the damage. “What I can see for myself is that everything has burned down.”
“There must have been fires deliberately set in several different places, it is not possible otherwise,” he added.
Fights lead to fire
Lalande said that the blaze had been started on Monday after a fight broke out between migrants that left six injured with knife wounds.
French press agency AFP reported that fights between migrants continued late through the night on Monday, which resulted in the deployment of riot police on site.
Tension between migrants at Grande-Synthe had increased as its population swelled due to the government evacuation and destruction last October of the migrant camp near Calais, some 40 kilometres away.
Some 7,000 migrants were living in the Calais camp, known as the “jungle”, when it was evacuated. Many of the migrants who came to Grande-Synthe after their previous home was bulldozed to the ground were Afghan, which caused friction with the camp's mostly Iraqi and Kurdish population, according to witnesses on the scene.
Migrants trying to reach the United Kingdom (UK) have set up informal camps and settlements on France’s northern coast, where Grande-Synthe and Calais are located, since the early 2000s.
However, in 2016, Grande-Synthe mayor Damien Carême allowed the international aid group Doctors Without Borders (MSF) to open an official humanitarian camp there, to the objection of the central government.
French officials had said in March that they were planning to dismantle the camp following violent clashes between migrants there.
The issue of squalid camps has led the United Nations (UN) to condemn the French government for failing to provide inadequate housing and basic services.
It has also been a point of contention between France and Britain, as many of the migrants in the region’s camps seek to reach the UK by sneaking into trucks or ferries crossing the English Channel.