Some five million people need urgent aid in Ethiopia, Oxfam estimates
Rains across swathes of East Africa have failed for the sixth year in a row, leaving millions of people facing hardship, Oxfam has warned.
The charity says Somalia's drought is the worst for 20 years, and November rainfall was less than 5% of normal in parts of Kenya and Ethiopia.
Oxfam says the next rains in hardest-hit areas are not due until April.
The UN has already said it is aiming to feed 20 million people in East Africa over the next six months.
It says the drought and rising food prices in East Africa are causing severe hardship.
Oxfam highlights large parts of the Turkana region of northern Kenya as having just 12mm of rain in the last three months - leaving almost one person in three malnourished.
The charity also says the Central Highlands and the Ogaden region of Ethiopia, and virtually the whole of Somaliland have also received less than 5% of normal rainfall in November.
The crisis is most severe in parts of Somalia, where worsening conflict and the drought have left 3.6 million people - nearly half the country's population - in need of aid.
"The rains were many people's last hope, but they have failed again," said Oxfam's deputy humanitarian director Jeremy Loveless, who has recently visited Somaliland.
He said more must be done to help communities cope with the dry years through long-term rural development and investing in national agriculture.
"But in the short-term lives are at stake and emergency aid is needed now," Mr Loveless said.
The aid group said 1.5 million cattle, goats and sheep have already died in Kenya, Tanzania and Uganda - putting many people's livelihoods at risk.
The surviving animals are being sold off at rock-bottom prices.
To make matters worse, farmers are leaving the land to search for a living in cities already suffering from high unemployment, the charity says.