Thousands of migrants in the "Jungle" camp in the French port city of Calais face eviction unless a last-ditch judicial bid goes in their favour.
They have until 20:00 (19:00 GMT) to move their makeshift homes in the southern half of the camp - or face bulldozers coming to clear them.
A court in Lille will rule on a challenge by charities to the eviction.
Charities say the migrants are being evicted in mid-winter with no adequate alternative accommodation provided.
French and British officials want to reduce the number of migrants in Calais and deter others from heading there in the hope of reaching the UK.
Conditions in the camp are squalid and its sprawling presence has become a controversial issue in both France and the UK.
The judge ruling in the Lille case was due to visit the camp on Tuesday morning.The southern side of the camp, says the BBC's Thomas Fessy, constitutes the cultural and commercial heart of the camp, with makeshift communal facilities such as a centre for teenagers.
French local officials and migrant lobby groups have different estimates of the number of people who would be affected if it is cleared.
The officials say the figure is between 800 and 1,000, while Help Refugees carried out its own "census" which it says revealed 3,455 residents in that zone.
The activist group says hundreds of unaccompanied children will also be affected.
"Our concerns remain with welfare of the unaccompanied minors," Help Refugees says.
"We have had no assurances from the French authorities that they will conduct assessments to determine best interests of these children and ensure proper safeguarding is in place before removing them from the camp and the communities they know and trust."
But Interior Minister Bernard Cazeneuve said the eviction would be done "progressively, by persuasion and with respect for people's dignity".Evicted residents face a choice, either to move into refitted shipping containers set up in the camp, or move to a migrant accommodation centre elsewhere in France.
Some migrants have baulked at moving into the shipping containers, saying they are unfit for purpose. Help Refugees says there are only 300 spaces left in the containers.
Leaving Calais is also a difficult decision for migrants set on reaching the UK, where many have relatives.
