Annan was scheduled to start his visit on Tuesday to Niger's second city, Zinder, in the south of the sub-Saharan country, where President Mamadou Tandja would meet him, media reports said.
The UN chief was then due to go the paediatric service of Zinder hospital, where starving children are treated, and then to a nutrition centre run by Medecins sans Frontieres (Doctors without Borders) in a village called Madara.
MSF, a French-based specialist charity with branches in several European countries, was among a number of bodies to draw the world's attention to the deadly scale of famine in Niger.
The country had already been hit by desertification and by locust swarms this year that wreaked havoc on crops across a wide swathe of northern Africa.
Annan, according to the official UN programme, was also due to meet representatives of several humanitarian bodies briefly before heading on Wednesday for Niamey, the capital, for formal talks there with Tandja and representatives of UN agencies operating in the country.
The Zinder region, once the food basket of the country for staple crops, was one of the hardest hit by drought and creeping desert, as well as by locust swarms which devastated crops.
According to the UN, more than 2.5 million people remain "in a vulnerable situation" in Niger, including 32,000 children in "deadly danger".