"Provinces in the east of Chad are among the country's most vulnerable zones with poor access to basic services, and the arrival of refugees drastically exacerbates the need," Action Contre La Faim (ACF), or Action Against Hunger, said in a statement.
The United Nations had warned in March that life-saving food aid for hundreds of thousands of people pouring out of war-torn Sudan would grind to a halt in April without international funding.
The UN World Food Program, WFP, appealed for $242 million in donations to avoid disaster and continue supporting 1.2 million Sudanese refugees, with the approaching rainy season threatening to cut off road access for humanitarian deliveries in eastern Chad.
The vast central African state was already one of the poorest in the world with 1.4 million people displaced internally or from other neighboring countries.
"It is urgent for donors to guarantee sustainable financing of the humanitarian response," said ACF's Chad director Henri-Noel Tatangang. It was currently covered only 4.5 percent of requirements, he added.
FILE - Refugees fleeing the conflict in Sudan queue with their jerrycans to queue to collect drinking water from the Doctors Without Borders (MSF) distribution point at the Ourang refugee camp in Adre on December 7, 2023.
Sudan's vast western region was still reeling from the carnage of a 2003 conflict when a new war broke out last April between the army and the paramilitary Rapid Support Forces (RSF).
The latest violence has uprooted eight million people in Sudan, adding to the more than 400,000 refugees who had already fled to Chad between 2003 and 2020, according to the UN.
That figure has risen to 900,000 today with 88 percent of them women and children.
ACF sounded an alert over the 480,000 cases of severe child malnutrition expected in the year to September 2024.
Chad's transitional president Mahamat Idriss Deby Itno declared a "state of food and nutritional emergency" throughout the country in February.