As many as 750,000 people could die as Somalia's drought worsens in the coming months, the UN has warned, declaring a famine in a new area.
The UN says tens of thousands of people have died after what is said to be East Africa's worst drought for 60 years.
Bay becomes the sixth area to be officially declared a famine zone - mostly in parts of southern Somalia controlled by the Islamist al-Shabab.
Some 12 million people across the region need food aid, the UN says.
The situation in the Bay region was worse than anything previously recorded, said senior UN's technical adviser Grainne Moloney.
"The rate of malnutrition [among children] in Bay region is 58%. This is a record rate of acute malnutrition," she told journalists in the Kenyan capital, Nairobi.
This is almost double the rate at which a famine is declared.
"In total, 4 million people are in crisis in Somalia, with 750,000 people at risk of death in the coming four months in the absence of adequate response," the UN's Food Security and Nutrition Analysis Unit (FSNAU) says.
Half of those who have already died are children, it says.
Neighbouring Djibouti, Eritrea, Ethiopia, Kenya and Uganda have also been affected by the severe lack of rain.
See also BBC News - East Africa Hunger Crisis.
