Recent weeks have seen targeted attacks on civilians, rapes and child abduction as the conflict between government forces and rebels becomes more violent.
The conflict in the state has been raging since the end of 2013 when opposition politicians were accused of an attempted coup on President Salva Kiir.
The civil war has left thousands fleeing their homes, compelled to eat wild food and drink dirty swamp water.
Predictions from the United Nations suggest the fighting has displaced more than 100,000 people and blocked humanitarian aid deliveries for some 650,000 people.
Thousands of people have fled the violence
More than 3.8 million, a third of the country's population, do not have sufficient food, the UN said.
Christian Aid said it's partner working in the Unity State is planning how it will start delivering aid again as soon as possible.
It said aid workers were considering dropping aid from the skies to get vital supplies like plastic sheeting for shelter and water purification tablets to affected areas.
Jolly Kemigabo, Christian Aid country manager in South Sudan, said: "The situation here is now critical. The fighting is directly affecting certain areas in the north but it is also having an impact throughout the country.
"Household food stocks have run out, cultivation is down and our currency has lost value so now people are spending 80 per cent or more of their income on food.
"It seems the world has ignored South Sudan for 18 months but with no sign of an end to the conflict, we desperately need more funding to respond to this humanitarian crisis".
