Fires are raging across parts of the "Jungle" migrant camp in Calais, three days into a French operation to demolish it.
It was unclear who set the dozens of fires overnight and in the morning.
The clearance began on Monday and about 4,000 migrants - out of some 7,000 - have been taken from the squalid camp to shelters around France.
The prefect of Pas-de-Calais said authorities now expected to finish the evacuation operation on Wednesday.
The camp has become a key symbol of Europe's migration crisis, with its residents desperate to reach the UK.
The BBC's Simon Jones, at the camp, says huts were set on fire overnight on the main street leading into the camp, leaving them in ashes.
He says this may have been a last act of defiance from migrants who did not want to leave and did not want to see their shelters taken down by the authorities.
Many of the makeshift shops that had been set up were destroyed and a London bus used by a charity to help women and children was torched.
More police are now being deployed to the site.
The prefect of Pas-de-Calais, Fabienne Buccio, told BFMTV is was "a tradition among the migrant population to destroy their homes before leaving".
However, the Calais police commissioner said he had been told by migrants that the fires were started by activists.
Camp resident Mahmoud al-Saleh told Agence France-Presse: "There were several fires overnight. Every time one was put out, another would erupt. It was clearly intentional.
"The firefighters came late. For a long time it was just us, migrants and volunteers, fighting the fires."
Dorothy Sang, of the charity Save The Children, told the BBC: "We know that hundreds of children slept in the Jungle last night, under the bridge, while fires were burning around them.
"We know that lots of them ran. It's a really, really dangerous situation for children right now."
More migrants joined queues on Wednesday for buses to take them out of the camp, with the situation calmer than the jostling of the previous morning.
Crews had begun dismantling the Jungle with sledgehammers on Tuesday. Workers in hard hats and orange jumpsuits pulled down unoccupied tents and shacks.
The work was carried out mostly by hand, and in a low-key manner, as officials believed sending in bulldozers would send the wrong message.
By the end of Tuesday, about 3,000 migrants had been moved out on coaches to centres across France, while another 1,000 unaccompanied minors had been given accommodation in containers near the Jungle.