The global children's charity, Save the Children, has warned that "thousands of others, including children, are likely to have fled to the remote bush; vast swampy areas where people will likely have no shelter and will be living under trees, will be forced to drink stagnant water, and where they will have no access to humanitarian support."
Aid agencies have noted that "access to food remains limited for displaced people sheltering in UN bases around the country, and there is a need for distribution of basic food and nutrition supplies. Food needs are particularly pressing in Bor and Bentiu."
In northern Unity State, three cases of measles have been reported since the fighting broke out. According to UN sources, thousands of children below the age of 15 will receive measles and polio vaccine at the UNMISS Tomping base in Juba.
Who are the most vulnerable?
The conflict has left women and children highly vulnerable to abuse. An aid worker who sought anonymity told IRIN there are increasing cases of gender-based violence including rape, and some parents have lost track of their children in the congested camps.
"It is a bad situation and many women are exposed to violence and many are being raped. The ethnic nature of this violence and suspicion among communities has made it extremely dangerous and we have had cases where women are attacked based on their ethnicity," she said.
Save the Children has warned that thousands of children might have been separated from their parents, "with many surviving on their own in very remote and hard-to-reach areas. Save the Children is highly concerned for their safety and welfare, many of whom have witnessed their parents being killed and their homes looted or destroyed".
How has insecurity hampered humanitarian efforts?
Insecurity remains the biggest challenge to humanitarian operations in South Sudan where fighting is still continuing, and increasingly marked by ethnically targeted violence between the Dinka community of President Salva Kiir and the Lou Nuer of his political rival and former vice president, Riek Machar.
In Bor, the capital of Jonglei State, which has become the focus of the violence, UNICEF country representative, Iyorlumun Uhaa, told IRIN that insecurity had hamstrung efforts to reach displaced children.