From civil war and urban gang violence to drought, some humanitarian crises around the world receive less media attention and donor funding than others and are less visible.

Below are the top five humanitarian crises of 2015, in no particular order, which aid agencies say deserve more attention on the world stage:

* CENTRAL AMERICA's HIDDEN DISPLACEMENT

Rampant gang violence, poverty and the lack of jobs push hundreds of people a month to leave the 'Northern Triangle' nations of El Salvador, Honduras and Guatemala and seek work and refuge in the United States and other Latin American countries.

In El Salvador and Honduras - which have the world's highest murder rates - entire city neighbourhoods are controlled by powerful street gangs, known as maras. They use extortion, sexual violence against girls and women, threats, killings and forced recruitment of children to exercise control.

"We have a situation that affects the lives of thousands of people because of widespread violence related to organized crime. What you have here is forced displacement," said Vicente Raimundo, head of the European Union humanitarian aid department (ECHO) regional office for Central America, Mexico and the Caribbean.

"Our concern is for those who are fleeing their homes because they are under threat, their relatives have been killed or they fear they are next on the list. They need to be protected. This is a big issue and we need to do more," he told the Thomson Reuters Foundation in a telephone interview from the Nicaraguan capital Managua.

To escape gang violence, families often first move from their homes to other neighbourhoods or cities within their own country, then seek refuge abroad, increasingly in Panama and Costa Rica.

"This is a hidden and urban phenomenon that is invisible and difficult to see. But it doesn't mean it doesn't exist," Raimundo said.

The United Nations refugee agency (UNHCR) said in October it had recorded a nearly five-fold increase in asylum seekers arriving in the United States from the Northern Triangle since 2008.

* SOUTH SUDAN REFUGEE CRISIS

South Sudan, which gained independence from Sudan in 2011, plunged into civil war in December 2013 when a political crisis triggered fighting between forces loyal to President Salva Kiir and rebels allied with his former deputy Riek Machar.

The conflict has reopened ethnic faultlines that pit Kiir's Dinka people against Machar's ethnic Nuer. A peace deal was signed in August but the two sides have repeatedly accused each other of violations and clashes continue.

Two years of civil war have killed more than 10,000 people, forced 1.6 million to flee their homes, some hiding for long periods in the bush and swamplands to escape fighting, and 185,000 to seek shelter in U.N. bases.

Nearly 650,000 have fled to neighbouring countries, according to U.N. figures.

The world's youngest nation also faces hunger. An estimated 2.4 million people are severely hungry, and in Unity state, some 30,000 people are at risk of famine, largely cut off from aid that can only reach them by air drops.

"South Sudan is very difficult for several million people facing food insecurity and conflict. But it gets very little in terms of international spotlight," said Shaheen Chughtai, deputy head of humanitarian policy and campaigns at aid agency Oxfam.

South Sudan's refugee crisis is also one of the world's most under-funded humanitarian crises. As of December, only 19 percent of a $659 million U.N. appeal for a South Sudan regional refugee response plan including Kenya, Uganda and Ethiopia, had been funded, the fourth least funded U.N. appeal.

* CENTRAL AFRICAN REPUBLIC CONFLICT

The Central African Republic (CAR), a former French colony, descended into chaos in early 2013 when mainly Muslim Seleka rebels seized control in the majority-Christian nation, where its abuses led to reprisals by Christian anti-balaka militias.

Thousands of people have been killed in the ensuing inter-religious violence in the capital Bangui and across the country.

"The recent visit of the Pope put CAR on the map for an instant but few people know the name of its capital or where it is. The international community isn't interested in CAR," said David Cantero, head of the medical aid group Doctors Without Borders (MSF) for Spanish-speaking countries in South America.

An estimated 2.7 million people - over half the population - need food, drinking water, health services and medicine, the U.N. Office for the Coordination of Humanitarian Affairs says.

The number of people forced to flee their homes within the country to escape fighting has risen by nearly 20 percent, to 447,500 in November from 378,400 in September, the UNHCR says.

In addition half a million people have left the country, around half of them fleeing to neighbouring Cameroon.

Many of the internally displaced people are trapped in enclaves, beyond the reach of state authorities and French and U.N. peacekeepers, some in fiefdoms controlled by warlords.

On Dec. 13 voters braved fighting and intimidation by armed groups to cast their ballots in a constitutional referendum seen as a crucial step toward ending the violence. Two days later a Seleka leader declared an autonomous state in his northeastern stronghold.

* YEMEN'S WORSENING HUMANITARIAN CRISIS

Yemen has been unstable since a 2011 revolt toppled veteran president Ali Abdullah Saleh, and plunged into civil war last year when the ex-leader joined forces with the Houthis to seize power, triggering a Gulf Arab military intervention.

The warring parties have started a UN-sponsored peace talks in Switzerland in a bid to end months of fighting that has killed nearly 6,000 people.

"Yemen has struggled to get the kind of attention it deserves in the mainstream western media," said Oxfam's Chughtai.

Saudi-led warplanes began bombing positions of the Houthis and their Yemeni army allies in March. The U.N. says at least 5,800 people, nearly half of them civilians, have been killed since the air strikes began, and aid agencies say the humanitarian situation has got worse.

More than 21 million people in Yemen require some kind of humanitarian help to survive - about 80 percent of the population, including 2.3 million people who have been uprooted.

"The suffering that this conflict is inflicting on people is heartbreaking. I hear first-hand accounts of it whenever I speak with women, children and elderly people who have made the perilous crossing to reach Djibouti, Ethiopia and Somalia," Claire Bourgeois, UNHCR's regional refugee coordinator for Yemen, said earlier this month.

* GLOBAL IMPACT OF EL NINO

From Ethiopia, Malawi, Papua New Guinea to Honduras and Haiti, tens of millions of people around the world are suffering the impacts of a strong El Nino weather pattern.

El Nino - a warming of sea-surface temperatures in the Pacific - affects wind patterns and can trigger massive floods and devastating droughts in different parts of the world, reducing harvests and making it hard for people to feed themselves.

As the impact of El Nino is so dispersed across the world and has affected regions in different ways, it is difficult to capture and understand its true scale, aid agencies say.

Experts say the impact of the current El Nino, which will intensify into 2016, could be the worst on record since 1997-98.

Up to 50 million people across the world will face water and/or food shortages related to El Nino in 2016, Oxfam says.

"In reality this is not one crisis but many," Oxfam said in a briefing paper published earlier this week. "The current international focus is understandably on hardest-hit countries but the international response needs to go much further to ensure other countries do not follow suit."

Around 2.3 million people in Central America, mostly subsistence farmers and their families, will need food aid because of widespread damage to crops and rising food prices due to a prolonged drought made worse by El Nino, according to the U.N. World Food Programme (WFP).

More than 10 million Ethiopians, one in 10 of the population, will not have enough to eat next year due to the effects of a crippling drought made worse by El Nino, the charity Save the Children says.

In Southeast Asia, El Nino is typically associated with drought and has helped fuel wildfires in Indonesia, among the worst on record. Other southeast Asian countries, particularly India and Sri Lanka, face severe flooding caused by heavy rains in 2016, the UN says.-Reuters