Turkish Prime Minister Recep Tayyip Erdogan toured famine-hit Mogadishu Friday on the first visit by a major leader in almost 20 years, calling the extreme drought ravaging Somalia "a problem for all humanity."

Somalia has been the worst affected in the Horn of Africa by a prolonged drought and the United Nations has officially declared a famine in five regions of the country, including the capital Mogadishu.

"This is not only Turkey's problem. This is a problem for all humanity. The tragedy going on here is a test for civilization and contemporary values," Erdogan told reporters.

The Turkish premier, accompanied by his family and four ministers on the visit, called on the world to take action.

"The civilised world must successfully pass this test in order to prove that Western values are not made up of empty rhetoric," he said.

The visit follows the Organisation of Islamic Cooperation's Wednesday meeting in Istanbul which pledged $350 million to assist the drought- and famine-stricken Somalis.

But Erdogan said the meeting did not meet expectations: "We had greater expectations at that point, but if you ask me if we fulfilled those expectations I cannot say yes."

"I believe it is necessary to make investments here," he added, promising that Turkey will fund infrastructure projects including restoring a hospital, building schools, drilling wells and rebuilding the road from Mogadishu airport to the city.

Somali President Sharif Sheikh Ahmed commended the Turkish government's efforts to help.

"We are very grateful to the Turkish government and people for the tireless assistance they are giving. We will never forget how they stood by our side as friends in this time of humanitarian disaster," he said at the press conference.

Erdogan and his host visited a field hospital established by the Turkish government as well as a former hospital turned military base that Turkey wants to rehabilitate as a hospital.

Security was tightened throughtout the day in Mogadishu, a city that has been battered by a bloody insurgency as Al-Qaeda-affiliated Shebab rebels fight to unseat the Western-backed Somali government.

Erdogan and his delegation flew out of Mogadishu in early evening, an AFP reporter said.

A recent influx of more than 100,000 people seeking help has altered Mogadishu's landscape, with hundreds of small stick and plastic shelters springing up in open spaces.

The city's hospitals have also been overstretched with emaciated adults and malnourished children, many of whom have succumbed to the harshness of the Horn of Africa's worst drought in decades.

Relief agencies have boosted aid delivery to the affected population, but insecurity in one of the world's most dangerous countries is hobbling a wider reach.

Rising cases of cholera and acute diarrhoea have compounded the misery of Somalis, the World Health Organisation and the UN children's agency UNICEF said Thursday.

Some 4,272 cases of cholera or acute watery diarrhoea have been reported in Mogadishu's Banadir hospital alone since January, the agencies said.

The disease has also been confirmed in four southern Somalia regions and the number of cases has risen.

Cholera is endemic in Somalia but the last major outbreak dates back to 2007 when 67,000 cases were recorded.

Aid agencies have warned that the whole of southern Somalia could be hit by famine in the coming weeks.

The UN's food monitoring unit has described Somalia as facing the most severe humanitarian crisis in the world and Africa's worst food security crisis since the country's 1991-1992 famine.

Much of southern Somalia, including the majority of regions declared to be in famine, remains under the control of the extremist Shebab militia.

Thousands of Somalis have sought refuge in Ethiopia and Kenya, but life in camps in the neighbouring countries remains difficult due to congestion, threats of disease and insecurity.

The drought has also hit parts of Ethiopia, Djibouti, Kenya and Uganda.