Between November 1 and January 27, 559 cases of the bacterial disease meningitis were reported in Niger's Zinder region, including 111 that were confirmed in a laboratory to be meningitis, the World Health Organization (WHO) said.
During the same period a year earlier, 231 cases were reported.
In the current outbreak in Niger, people under 20 years of age have been most affected, with most cases seen among children aged 10 to 14. Seventy-six cases were seen among children aged four and younger, the WHO said.
Six strains of the Neisseria meningitidis germ are notorious for causing epidemics.
But early symptoms -- headaches and fever -- can be difficult to spot as they are similar to other common ailments.
The Sahel nation is located in Africa's so-called meningitis belt, experiencing seasonal outbreaks every year.
Nearly 1,400 deaths have been recorded in the country since 2015.
But the UN health agency voiced concern, saying the ongoing outbreak shows "both an increased number of cases and an increased growth rate" compared to the previous seasons.
Most of the lab-confirmed cases in the Zinder region were due to the serogroup C of N. meningitidis, or NmC, the WHO said in its statement.
It pointed out that the region shares a border with Jigawa State in Nigeria, where a NmC outbreak is also ongoing, "confirming the risk of international spread".
"The simultaneous occurrence of other epidemics, insecurity and population displacement, all in the context of a protracted humanitarian crisis, are likely to contribute to the spread of the outbreak in other countries of the West African sub-region," the WHO warned.
The organization said it assessed the risk from the outbreak as "high" at the national level in Niger, and "moderate" at the West African regional level, but said that the risk of it spreading beyond the region was "low."
Meningitis is an infection of the lining surrounding the brain and spinal cord, transmitted through respiratory droplets or throat secretions from those infected.