"In all we have 847 people, including 40 women and 74 unaccompanied children," Agadez municipal authority said late Thursday.
The child protection ministry has taken care of the minors, it said.
A humanitarian source said "some 800 migrants" arrived at the border at the start of the week after being "escorted" there by Algerian officials.
The migrants, mostly from Niger, will be given medical care and basic necessities, the source said.
Since 2014, Algeria has expelled tens of thousands of migrants from west and central Africa, according to the United Nations.
Many of the travellers take the dangerous route across the Sahara in a bid to reach the Mediterranean coast and from there to cross to Europe.
The French charity Doctors without Borders (MSF) has recorded a growth in the numbers thrown out of Algeria in recent years.
Some 23,171 were expelled in 2020, 27,208 in 2021 and 14,196 from January-May this year, MSF says.