Violence between armed groups in Upper Nile state and other flashpoints has crippled essential services, triggered food insecurity and worsened disease outbreaks, including cholera - forcing some to be displaced repeatedly.
Roughly 65,000 have been internally displaced in Upper Nile state alone.
Access to aid in conflict hotspots is limited, with fighting and movement restrictions cutting off assistance.
Lifesaving supplies, including medicine and healthcare to curb rising cholera cases, have halted, while rains threaten to worsen the crisis, flooding roads and driving up transport costs.
South Sudan has also absorbed over a million people fleeing conflict in Sudan.
Regional crisis
Another 103,000 South Sudanese have sought refuge in neighbouring countries, pushing the total number of South Sudanese refugees to 2.3 million.
"This emergency could not have come at a worse time," said Mamadou Dian Balde, UNHCR 's Regional Director for the East, Horn of Africa and Great Lakes region.
"Many of the refugees are seeking safety in countries which have challenges of their own or are already dealing with emergencies amidst ongoing brutal funding cuts, straining our ability to provide even basic life-saving assistance."
Despite the conflict in Sudan, 41,000 South Sudanese have sought refuge there - 26,000 in White Nile state, where over 410,000 South Sudanese already live, many repeatedly displaced due to ongoing violence in their host country.
The surge in arrivals in Sudan has created an urgent need for additional space, while essential services are overwhelmed due to cholera outbreaks and ongoing security challenges.
In the Democratic Republic of the Congo (DRC), 23,000 have arrived amid the country's own insecurity.
Some 21,000 South Sudanese have sought refuge in Ethiopia. Previously living in makeshift shelters along riverbanks near the border, new arrivals are now receiving UNHCR aid further from the border; however, infrastructure and services in the area remain severely overstretched, worsened by a cholera outbreak.
Uganda, which hosts one million South Sudanese refugees, has taken in 18,000 since March - a 135 per cent year-on-year increase. Nearly 70 per cent are children; many forced to take longer and more hazardous routes to safety.
Call for support
UNHCR is providing refugees with critical relief items, documentation and specialised support to survivors of gender-based violence.
But to provide necessary support for the next six months - including shelter, water, health and nutrition screening, as well as cash assistance - the agency requires $36 million.
Calling for an immediate end to hostilities, UNHCR urged all parties to spare civilians further suffering.
