Oxfam said it has begun an emergency appeal to raise $36 million to help more than 1 million of the most vulnerable people in the region, the BBC reported.
Oxfam said more than 1 million children are at risk of severe malnutrition in the Sahel region.
Malnutrition rates across Chad, Burkina Faso, Mali, Mauritania, Niger and northern Senegal are 10 percent to 15 percent and in some areas have risen beyond the emergency threshold level of 15 percent, Oxfam said.
The charity attributed the crisis to drought, high food prices and regional conflict.
In Chad, the situation has grown so desperate some villagers have been digging up ant hills to get to grain the ants have stored, the BBC said.
"Millions of people are on the threshold of a major crisis," said Mamadou Biteye, Oxfam regional director for West Africa.
"All signs point to a drought becoming a catastrophe if nothing is done soon. The world cannot allow this to happen. A concerted aid effort is needed to stop tens of thousands dying due to international complacency."
The BBC said recent fighting between rebels and the army in northern Mali has led to more than 100,000 people fleeing their homes and half of them enter Niger or other struggling countries.
Oxfam and Save the Children said in January thousands of people in East Africa died from famine last year because the international community did not heed early warnings.