This year's survey was unusual for the high number of "most forgotten crises", with experts also listing the Central African Republic, Lake Chad Basin, Yemen, Afghanistan, South Sudan, Burundi, Nigeria and, for the first time, Venezuela.

But Congo's "mega-crisis" barely made headlines, they said, even as the country gears up for landmark elections on Sunday which some fear could stoke further unrest.

"The brutality of the conflict is shocking, the national and international neglect outrageous," said Jan Egeland, head of the Norwegian Refugee Council.

"I visited Congo this year and have seldom witnessed such a gap between needs and assistance."

Congo, where 13 million people in a population of 82 million need help, also topped the annual Thomson Reuters Foundation poll in 2017, but agencies said the situation had deteriorated.

Six of 21 agencies polled named Congo as the most neglected crisis, including WFP, Norwegian Refugee Council, Oxfam, ActionAid, International Rescue Committee, and Christian Aid.

ActionAid's humanitarian advisor Rachid Boumnijel urged the international community to redouble efforts to end years of conflict characterised by sexual brutality.

"It's been a catastrophe for the country, and for women and girls particularly," Boumnijel said.

Christian Aid's head of humanitarian programmes Maurice Onyango said the violence had caused "large-scale trauma", with children witnessing parents and siblings being murdered.

An upsurge of fighting in the east of the mineral-rich country has also exacerbated the spread of the world's second largest Ebola outbreak, agencies said.

The Central African Republic, where armed groups control much of the country and 60 per cent of the population needs assistance, came a close second in the poll.

Listed as the most neglected by OCHA, UNICEF, MercyCorps, Plan International, and Caritas, the country has been racked by violence since mainly Muslim rebels ousted the president in 2013, provoking a backlash from Christian militias.

Armed groups are increasingly targeting schools, hospitals, mosques and churches, while attacks on aid workers have impacted a "chronically underfunded" humanitarian response, they said.

UN children's agency UNICEF said thousands of children had been trapped in armed groups or subjected to sexual violence.

"The crisis is growing increasingly desperate and resources are at breaking point," added UNICEF emergencies director Manuel Fontaine.

UN appeals for both DRC and CAR are less than 50 per cent funded.

"Central African Republic is in a death spiral," said Caritas Secretary General Michel Roy. "While governments and the world's media have turned their backs, we must not. It's the only hope CAR has left."

Australian Associated Press