The Belgian prime minister has urged France to find a solution to the sprawling camps sheltering thousands of Britain-bound migrants at its northern ports, saying the failure to do so was pushing growing numbers towards neighbouring Belgium.
As the refugee crisis has spread across Europe, numbers at Calais have swelled to around 4,000 migrants, and another camp has sprung up near Dunkirk. Both ports are ferry or train rides away from Britain.
Belgian Prime Minister Charles Michel wrote a letter to French counterpart Manuel Valls urging France to find a solution for the camps, a Belgian official said.
The two prime ministers will meet in Brussels on Monday.
France has tightened security around the makeshift camp at Calais and Belgian officials say that as a result, migrants are increasingly trying to reach Britain via neighbouring Belgium.
Since December, Belgian police have intercepted hundreds of migrants around the cargo port of Zeebrugge, which had previously not been affected.
"We want a concrete proposal by France on how to deal with the situation in Calais," a Belgian official told Reuters.
In August, Britain said it would contribute 10 million euros ($11 million) to increased French humanitarian assistance and a fast-track asylum process for the migrants at the camp.
The countries also tightened security around the port and Channel Tunnel and combined police operations against people smugglers. However, some migrants are still attempting the dangerous journey across, often at the risk of death.