Somalia's new leader has declared a national disaster for a prolonged drought that has forced about half of the country's population to seek urgent food assistance and sparked fears of a potential famine.

The announcement on Tuesday by President Mohamed Abdullahi Mohamed's office came a day after the World Health Organisation (WHO) warned that Somalia was at risk of its third famine in 25 years - the last one in 2011 killed some 260,000 people.

"The president has appealed to the international community to urgently respond to the calamity in order to help families and individuals to recover from the effects of the drought disaster to avoid humanitarian tragedy," read a statement from the presidency.

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According to WHO, more than 6.2 million people - half of Somalia's population - needed urgent humanitarian aid, including almost three million who are going hungry.

The agency said more than 363,000 acutely malnourished children and 70,000 severely malnourished children needed urgent, life-saving support.

Somalia is one of three countries, along with Yemen and Nigeria, on the verge of famine, which has already been declared in South Sudan.

Last week, the UN said more than 20 million people face starvation in the four countries, adding it needed $4.4bn by the end of next month to prevent "a catastrophe" of hunger and famine.

Aid agencies are concerned that the drought is exacerbating the country's on-going humanitarian crisis, while there are reports that the ongoing conflict with the al-Shabab armed group is further blocking access to food.

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Al Jazeera's Fahmida Miller, reporting from Dolow in southern Somalia, said she spoke to a number of refugees and internally displaced people.

"One woman we spoke to said it took her 11 days to find food and water. She said trying to get the assistance was near impossible because of threats from al-Shabab," she said.

"People here are losing livestock; rivers and water points have dried up and there is a huge issue around internally displaced people and refugees moving through Somalia looking for food and water," Miller added.

"As the rainfall is expected to stay low, there have already been a number of failed crop seasons and people can't grow their own food and have to move through the country looking for assistance."