An outbreak of highly contagious measles has put thousands of children in war-torn Somalia at risk of death or disability, the United Nations said on Tuesday.

Recent rates of infection are four times higher than the same time last year, and a vaccination campaign must be "urgently conducted to prevent thousands of avoidable deaths", the UN children's agency UNICEF and the World Health Organization (WHO) warned in a joint statement.

Since a devastating famine, poor rains and escalating conflict aid funding shortages less than three years ago, the acute crisis has led impoverished Somalia into another outbreak of renewed warnings and risks.

"We have a very high number of malnourished Somali children," UNICEF chief for Somalia Sikander Khan said.

"Malnourished children here are more susceptible to disease, and are more likely to die or suffer life-long disability such as blindness, deafness or brain damage as a result of contracting measles."

WHO head for Somalia, Ghulam Popal, said the outbreak was "extremely alarming", warning that 10 percent of children infected could die from complications.

Although vaccinations have been given to around half a million children in recent months, some five million in total need protection, the UN said.

Immunization rates are as low as 15 percent in some parts of Somalia, mainly southern and central regions including areas where African Union troops are battling Al-Qaeda linked Shebab insurgents.

Less than a third of children aged under a year were vaccinated countrywide in 2013.

"Somalia was the hardest hit by extreme drought in 2011 that affected over 13 million people across the Horn of Africa, with famine zones declared in large parts of the war-ravaged south," according to AFP.

"One in five children dies before their fifth birthday with measles one of the main causes, according to the UN."

Aid agencies have been struggling to raise the measles campaign cost of some nine million dollars needed for other emergencies in the country.