"We are dealing with a scale of malnutrition which the United Nations defines as a `catastrophe out of control' - more than five people out of every 10,000 dying every day," said Ian Bray, a spokesman for Oxfam.
The Republic of Congo, a small, oil-rich former French colony, is dwarfed in international attention by its giant neighbour, the former Zaire, known as the Democratic Republic of Congo, which is also at war.
Speaking from Brazzaville, Oxfam's programme co-ordinator, Jos Koster, said: "I have never seen anything like this. Around 300,000 people fled into the forests north of Brazzaville last year. Now they are trying to return because they have no food and the wells are poisoned by corpses. On the way south, they are encountering unbelievable brutality. "We are trying to set up centres for the people who are leaving the forest but it is dangerous. For weeks we have been trying to go to Kinkala [60km north of Brazzaville] just to set up a centre so that everyone does not flood into Brazzaville."
Oxfam estimates that Brazzaville's population of 700,000 has swollen by at least 80,000 in the past year and that there are between 150,000 and half a million displaced people in the hinterland. They are now starving. With the livestock dead, humans are left with only grass and wild roots and leaves to eat.
Mr Koster estimated 25 per cent of infants are suffering from severe malnutrition.