Save the Children says more than seven million people are suffering from some form of malnutrition in a country that has a population of around 15 million.
Of those, more than three million are described as severely malnourished or starving.
The aid group’s country director Ibrahima Fall said the extent of the crisis was being grossly under-estimated.
‘The transitional government in Niger has appealed for urgent assistance but the response from other rich governments and international donors has been slow and insufficient,’ he said.
‘Far more children will die if we don’t act fast.’
Sky News was given pictures showing some of those being brought to the Aguie centre for emergency treatment.
Seventeen-month-old Tsahirou was a fragile bundle when he arrived.
Most of his short life has been spent fighting a seemingly never ending cycle of disease and malnutrition – so far without success.
His mother Salmey said the family’s food ran out 40 days ago and they have nothing left to eat.
Two-year-old Rahina was also given urgent treatment.
The small child struggles to breathe, but her mother Hadija said it was hunger that could kill her.
‘We grow crops to sell to feed ourselves, but we received little rain in the last growing season and it wasn’t enough,’ she said.
‘We didn’t harvest any beans or peanuts and the yield of millet was very small. There is no food left over from our last harvest. Really there is nothing.’