“More than 5,000 people have already reached N’Guigmi,” a town in southeastern Niger located near the lake and the Chadian border, a UN official told AFP.
Another 11,500 people are expected to arrive in the town, the official added.
A local journalist told AFP he estimated that “some 3,000 displaced people” had so far arrived.
Niger authorities last week urged Lake Chad residents to evacuate their islands by Monday, citing security fears.
The call came a week after an assault by Boko Haram that left at least 74 dead. It was the country’s heaviest loss since it joined a regional offensive against the militants.