South Sudan is reeling from an unprecedented humanitarian crisis a month after deadly clashes between government and opposition forces set off a fresh cycle of violence and displacements, the UN has warned.

About 6 million South Sudanese – more than half of the country’s population – are now in need of humanitarian assistance, with 4.8 million facing severe hunger.

“I am extremely concerned as the humanitarian crisis in South Sudan continues to deepen and spread, causing untold devastation to so many innocent [people],” said Eugene Owusu, the UN’s humanitarian coordinator for South Sudan.

In Juba, the most recent surge in violence has left hungry, displaced families with a heart-wrenching choice: to stay inside the UN camp for displaced people and watch their children starve, or to fetch food from outside but risk attacks by marauding soldiers. More than a hundred women driven out of the camp by hunger were raped in the aftermath of the most recent violence, according to UN figures.

Since last year, hunger has encroached on relatively stable parts of this war-ravaged nation. The region of Northern Bahr el Ghazal, left largely unscathed by the conflict, has recorded alarming malnutrition rates after erratic rains and pests devastated last year’s harvest. One in three children are now at risk of starvation, while hunger has forced tens of thousands to migrate across the border to Sudan.

Shortfalls in agricultural production have been compounded by a deep economic crisis, marked by deteriorating terms of trade and skyrocketing food prices. The most recent fighting in Juba has brought the flow of goods along the main trade artery from Uganda almost to a halt, further accelerating price hikes and sending ripple effects through markets across the country.

Experts fear that the country is on the brink of famine. An outbreak of disease could push mortality rates – one of three indicators used to define a famine – much higher.

“We know that food consumption is extremely stretched. We know that malnutrition rates are extremely high. The biggest fear now is that it will just take a disease like cholera, malaria or diarrhoea to ignite a famine,” said Joyce Luma, the South Sudan country director of the UN’s World Food Programme.

Hunger levels have also spiked in the capital Juba, where last month’s violence has forced thousands from their homes. More than 60,000 fled across the border to Uganda, while thousands sought shelter inside the already overcrowded UN’s protection of civilian (PoC) site.

Many of the newly displaced inside the PoC are still waiting to be registered for aid. “We have gone for weeks without being assisted,” said Emmanuel Taban, who fled to the UN’s base following July’s clashes. “The community used to give us small rations, but nowadays even they ran out of food and they can’t give us anything.”

Luma said that registrations in the Juba PoC were under way, but it would be another three weeks before new arrivals could expect their first food ration.

The WFP has struggled to meet rising needs across the country after its warehouses were looted last month, resulting in the loss of large stockpiles of food that could have sustained 220,000 people for an entire month.

The looting was an additional blow to a severely underfunded aid operation. Only 40% of this year’s $1.3bn (£1bn) UN appeal has been funded so far, a figure that will soon be revised upward to reflect additional needs arising from the recent surge in violence in the southern Equatoria and the Western Bahr el Ghazal regions.

Restrictions on movement and attacks against aid workers have further hampered relief efforts. Since the beginning of the year, the UN has recorded 261 incidents of violence against humanitarian staff or assets. Near the western town of Wau, aid workers were recently threatened at gunpoint while trying to reach displaced populations.

“Aid workers in South Sudan are here to serve the neediest. They cannot do so if they are under threat of injury, abduction, harassment, arrest or even death,” said Owusu.