Chad's interim President Mahamat Idriss Deby has signed a decree declaring a food and nutrition emergency.
"This decision follows the constant deterioration of the food and nutritional situation this year and taking into account the growing risk to populations if no humanitarian aid...is provided," read the decree.
The plea for aid comes before a meeting between African Union chairman Macky Sall and Vladmir Putin to discuss Russian grain supplies.
The United Nations has warned that 5.5 million people in Chad - more than a third of the population - will need humanitarian assistance this year.
The World Food Programme said in March that some 2.1 million Chadians would be "severely food insecure" during the dry weather season that starts this month.