The attackers arrived in the Maza-Kuka community of Mashegu local government area at roughly 5 a.m., two residents told Reuters on Monday.
"They came and went straight to the mosque and shot at worshippers without sparing anyone," resident Abdulganiyu Hassan said.
Hassan said they abducted more than 10 others. Bello Ayuba, another resident and witness, said at least 20 were wounded.
A Niger state police spokesman did not immediately respond to calls or messages seeking comment.
Since the beginning of this year, the northwestern regions of Nigeria have witnessed attacks by gunmen and the domination of the terrorist group "Boko Haram" over a number of cities in the state of Niger.
ZZ/PR