They were reportedly caught as they were leaving the northern town of Arlit before dawn in five different vehicles.
The migrants - mainly men, with some women and a few children - are believed to be from Nigeria and Niger.
It comes days after 92 migrants died of thirst when two trucks broke down carrying them across the Sahara to Algeria. Niger lies on a major migrant route between sub-Saharan Africa and Europe.
Those arrested yesterday are now reportedly being held by police in Arlit.
The government announced on Friday a plan to close illegal camps in northern Niger - which it referred to as "ghettos" - and said those involved in trafficking migrants would be "severely punished".
The country has been holding three days of mourning after the bodies of 52 children, 33 women and seven men were discovered on Wednesday. Another five from the same convoy had been found several days earlier by the army.
Most of the dead were from the southern Niger district of Kantche.
Many of the victims were in an advanced state of decomposition and had been partly devoured by animals, probably jackals.
About 5000 African migrants are said to be stranded in illegal camps in the northern town of Agadez alone.
Most of these migrants - having paid large sums of money to traffickers - are waiting to cross the hundreds of kilometres of desert into Libya or Algeria, from where they can take boats to Europe in the hope of a better life there.
Niger has said that migrants found to be in the illegal camps will be handed over to international aid agencies.
Head of the International Office for Migration in Niger, Abibatou Wane, welcomed the action by the government but warned migrants should only be repatriated to their home countries on a voluntary basis.
Many people emigrate to flee poverty in Niger, ranked by the United Nations as the least developed country on earth. Some work in neighbouring Libya and Algeria to save money before returning home.
The networks which send trucks across the desert also attract migrants from other countries in West Africa who dream of a more prosperous life in Europe.
Many of the people-smugglers are from nomadic groups who have seen their traditional pastoral lifestyle destroyed by droughts since the 1970s, according to a UN report published in February.
More than 32,000 people have arrived in southern Europe from Africa so far this year.
A crackdown by Spanish authorities has largely closed a route from the West African coast to the Canary Islands which drew tens of thousands of migrants in the mid-2000s.
Instead, most now try to make the Mediterranean crossing from north Africa to southern Europe, many losing their lives when their rickety boats are wrecked.
More than 500 people are believed to have died in two shipwrecks off southern Italy this month.