International donors have promised more than $600m in aid to South Sudan at a conference in the Norwegian capital, Oslo.
The meeting on Tuesday is aimed at averting a famine threatening four million people in the world's youngest country.
"This figure represents just about a doubling of the available funds for the humanitarian crisis in South Sudan," said Norway's Foreign Minister Boerge Brende at the close of the conference on Tuesday.
The amount is in addition to the more than $500m already pledged by donors, but the combined amount still remains short of the $1.8bn the UN says the country needs to avoid famine, the AFP news agency reported.
The meeting of donors follows months of conflict between rebels and government forces, in which UN bases have come under attack.
"It's astonishing how much damage has been done: cities destroyed, lives shattered, empty markets, traders are now gone, kids left alone," UN humanitarian coordinator in South Sudan, Toby Lanzer, said.
According to the UN, around seven million South Sudanese may eventually need humanitarian aid.
At least 50,000 children are at risk of dying from malnutrition, according to UNICEF and 740,000 children under the age of five are at severe risk of "food insecurity".
The organisation warned that many in the country had already resorted to eating wild food such as plant bulbs and grass to avoid starvation.
Al Jazeera's Malcolm Webb, reporting from Malakal in South Sudan, said that while many people were safe inside UN camps, thousands more were in refugee camps in areas difficult to access, not controlled by the UN.
The situation is likely to worsen with the arrival of the rainy season, which will render existing roads and landing strips harder to use, complicating the distribution of aid.
Warnings about famine in South Sudan come as the World Health Organisation (WHO) said that at least nine people had died in a cholera outbreak in the country.
The organisation said there were 138 cases in and around the capital, Juba. The disease can kill in days if not treated fast enough.