"We don't have the additional money to cope with the extra needs in terms of sanitation or schooling. It goes beyond our budget," said Arlit's Mayor Abdourahamane Mouali.
"But the migrants are there, and we have to deal with the situation, only from a humanitarian point of view," he added.
In 2015, Niger approved a law based on the 2000 Palermo Convention on human trafficking criminalising support for illegal border crossings and for unauthorised stays on its territory.
The law wiped out a flourishing part of the local economy, which provided transport, food and shelter to the migrants.
IOM investing in stabilisation programmes
The IOM, the biggest international humanitarian organisation in Arlit, is investing in so-called stabilisation programmes such as water wells, sanitation and job creation schemes that help to show local people that migrants are not being unfairly favoured.
But the needs are huge. In 2022, the number of stranded migrants seeking help from the agency rose by 35 percent to more than 17,000.
Funding from international donors meanwhile has declined, forcing many schemes to end, according to local officials.
Many locals are convinced that the population explosion has led to crime, including frequent armed attacks.
"The migrants leave us in peace. They even respect Nigerien law more than Nigeriens do. It's the gold miners who are the source of the problems," said Issa, the trader.
Five soldiers on Sunday were killed in an ambush by unidentified gunmen as they were escorting a convoy of miners from the gold rush site of Tchibarakaten, a security source and media said.
"Quantities of gold were probably carried off," according to a local elected official.
Arlit also lies several hundred kilometres from Mali, the nexus of a bloody militia insurgency that has expanded into Burkina Faso and South-western Niger.
"For the time being, the region is stable, but we don't know how long it will last," said Ibrahim Rixa Issa, a vice chairman in the regional council.
"We only have two border posts on a line of 2,000 kilometres, and we don't have enough money to do air surveillance," said the region's governor, Magagi Maman Dada.