Ruling party candidate Mohamed Bazoum is seen by many as the favourite after leading in the first round on December 27 with 39.3 percent of the vote. Polling stations opened at 0700 GMT and will close at 1800 GMT (8 am to 7pm) local time.
A dual national was arrested near the Syrian border with her two children and identified as a Daesh member. NZ PM Ardern urged Australia to consider the welfare of the children who were "born in a conflict zone through no fault of their own".