Somalia's transitional government welcomed a UN declaration that famine has hit two southern regions of the war-torn nation, saying they hoped it would boost aid to the stricken areas.

Up to 350,000 people are affected by famine in the rebel-held southern Bakool and Lower Shabelle areas, the UN announced in Nairobi.

"At least it is great that the world has recognised the magnitude of hardship the poor Somalis are facing," Abdulkadir Moalim Nur told AFP, a minister in the president's office.

"The acknowledgment of the severity in those regions may help the shortage of food by sending famine assistance including medicine by UN agencies," he added.

According to the UN, the extreme drought is affecting more than 10 million people in the Horn of Africa, in the most severe food crisis in Africa for two decades.

Both famine areas are controlled by Al-Qaeda inspired Shebab insurgents who are battling the weak Western-backed government but have authorised the return of foreign aid almost two years after expelling most relief groups.

Nur warned that other areas also remain at severe risk.

"There are other regions which are also very food insecure in southern and central Somalia," Nur said.

Thousands have fled into the capital Mogadishu, and aid workers there said they supported the famine declaration.

"We knew for a while that there was famine in the country, but we waited for the declaration of the UN," said Mohamed Yakub, a Somali aid worker.

"People are dying from a lack of food and medicine. First their crops were devastated by drought, then their animals died, and finally they lost the family they loved," he added.

"The decision is not only timely but is very much welcome," said Khadija Hassan, from a Somali woman's aid organization.

"I hope more women and children are saved by famine donations," she added.