Guterres said at a joint press conference with President Hassan Sheikh Mohamud that he was on a "visit of solidarity" to the troubled Horn of Africa nation, where five million people are facing high levels of food insecurity.
"I am also here to ring the alarm on the need of massive international support... because of the humanitarian difficulties the country is facing," he said, adding that he wanted to help build Somalia's security capacity and encourage its development.
The United Nations has launched a $2.6 billion call for humanitarian assistance, but Guterres said the appeal was only 15 percent funded.
Guterres's trip comes with the country in the grip of a calamitous drought that has driven many to the brink of famine, while the government is also engaged in a major offensive to put down a bloody Islamist insurgency.
The UN chief, who previously visited Somalia in March 2017, is due to hold talks with political leaders and visit a camp for internally displaced people, according to local media reports.
Five straight failed rainy seasons in parts of Somalia as well as Kenya and Ethiopia have led to the worst drought in four decades, wiping out livestock and crops and forcing at least 1.7 million people from their homes in search of food and water.
A report by the UN and the Somali government released in March said that drought may have led to 43,000 "excess deaths" last year, with children under the age of five accounting for half the victims.
While famine thresholds have not been reached in Somalia, the UN says about half its population will need humanitarian assistance this year, with 8.3 million affected by the drought.
"The crisis is far from over - needs remain high and urgent," the UN's resident coordinator for Somalia, Adam Abdelmoula, said last week in Geneva.
"Some of the most affected areas continue to face the risk of famine."
Adding to the woes, seasonal rains in March led to flooding that claimed the lives of 21 people and displaced more than 100,000, he said, while warning that the rains were unlikely to be enough to improve the food security outlook for many.
Somalia has been wracked by decades of civil war, political violence and a bloody insurgency by the Al-Qaeda affiliate Al-Shabab.
In a report to the UN Security Council in February, Guterres said that 2022 was the deadliest year for civilians in Somalia since 2017, largely as a result of Al-Shabab attacks.
President Hassan Sheikh Mohamud last year declared "all-out war" against the Islamist militants. n recent months, the army and the militias known as "Macawisley" have retaken swathes of territory in an operation backed by an African Union force known as ATMIS and US air strikes.
It also said in a statement issued by the information ministry that 70 towns and villages had been "liberated" from Al-Shabab, which has been fighting the fragile central government for more than 15 years.
It was not possible to independently verify the claims.
