The development agency warned that the situation in the west African region was "deteriorating fast".
It has raised £475,000 since the launch of its appeal in March but is asking supporters and major donors to consider giving more to deal with the scale of the crisis.
Food aid for nearly 250,000 Malian refugees in Burkina Faso, Mauritania, Niger and neighbouring states is set to run out in weeks, the World Food Programme has warned.
Christian Aid's head of humanitarian operations Nick Guttmann said: "There are 19 million people across the Sahel who are in dire need. More than a million children are at risk of severe acute malnutrition and an estimated three million are at risk of moderate acute malnutrition.
"Increasing numbers are entirely dependent on food aid for survival, particularly refugees who have fled from the conflict in Mali to neighbouring states, and people displaced within Mali itself.
"This is traditionally a lean time in that part of the world The first rains have come and new crops have been planted, but because last year's harvest was so poor due to the drought, even those who are not affected by conflict have nothing to tide them over."
The food crisis has been exacerbated by rising food prices and flash floods in some areas, which have destroyed crops, stores and homes.
Christian Aid is distributing rice and cereal to some of the 4.6 million in need in Mali, including those displaced by conflict and others already suffering shortages.
Food and nutrition training is being given to pregnant women and mothers of malnourished children in northern Niger.
In Burkina Faso, communities are receiving improved seeds to help them grow food despite the drought.
Christian Aid's head of media, Andrew Hogg, was in Mali on a fact-finding mission last week. He visited the government-controlled town of Konna in the north where desperate families have been trickling in from the rebel area, many with nothing more than the clothes they are wearing.
It reports that some people have been forced out by insurgents, while others have left through fear. There are reports of the widespread sexual abuse of women. Men suspected of being members of the military have been taken away and not seen again, Christian Aid says.
Partner agency GRAT (Groupe de Recherche et d'Applications Techniques) is focusing distribution on the most vulnerable, with some 50 tonnes of rice and cereal, and 10 tonnes of seed going to the internally displaced, and to host families.
A few kilometres in a suburb of the town of Sevare, Mayor Zeine Diallo said: "Many people are facing real starvation here. Rice and seed had been distributed to the most needy, but another 800 tonnes of rice are needed."
Djougal Tapily, an elder in the town of Bandiagara, survives with his wife and their family of six on millet supplied by Christian Aid partner Action Promotion Humanitarian (APH). A small breakfast bowl of the cereal uncooked is the daily allowance for two adults.
The 70-year-old said: "It keeps us alive but it is not enough. We are always hungry, but we have to manage what we have. Underneath my shirt I am very thin. Usually it is only this bad if the locusts come, I spend all my time worrying about how the family will be fed."