It's a crisis the world has largely ignored, despite some 20,000 deaths and an estimated 2.6 million people forced from their homes.

Northeast Nigeria is facing famine, the collateral damage from seven years of Boko Haram's deadly insurgency and a problem aid agencies have long been warning about.

Children are starving. Whole villages and towns in desperate need of assistance are out of reach because of insecurity and fighting, despite military gains in recapturing territory lost to the Islamists.

Aid agencies talk of a looming humanitarian catastrophe. Those there say it's already happening.

A soldier walks past a checkpoint in Bama, Borno state, Nigeria, August 31, 2016. Nigeria's military has liberated large swathes of land from extremist group Boko Haram, but a brutal Islamist insurgency has killed an estimated 20,000 people and displaced millions more since 2009. (Afolabi Sotunde/Reuters)

This week, UN Secretary-General Ban Ki-moon will make a renewed appeal for funding to stave off the crisis.

Some $559 million is needed between now and the end of the year to provide food, shelter and vital health care for those in need, not just in Nigeria but also in neighbouring Cameroon, Chad and Niger, where the violence has spread.

"It's devastating," said Doune Porter, from the UN children's fund UNICEF, speaking to CBC News from Nigeria's capital, Abuja.

Children are basically just clinging to life. - Doune Porter, UNICEF

"It's really bad…. For the immediate crisis, just in Borno state alone there's 244,000 children who will suffer this year from severe acute malnutrition. Children are basically just clinging to life."

Three months ago, UNICEF said one in five of those 244,000 — nearly 50,000 children under five — could die if nothing was done.

Estimates are of a possible 130 deaths every day. But money is needed, and with Nigeria's economy officially in recession, the funding is going to have to come from elsewhere.

"This is too big for the Nigerian government to handle, too big for UNICEF to handle on its own, too massive a crisis — and the world needs to mobilize," said Porter.

But with so many other humanitarian crises dominating the headlines, such as Syria and migrants in Europe, there's no guarantee the world will sit up and take notice.

Nigerian President Muhammadu Buhari, seen here speaking Sept. 21, 2016, at the Plaza Hotel in New York, where a business forum is focused on trade and investment opportunities on the African continent. (Drew Angerer/Getty Images)

Nearly three years ago, Nigeria became Africa's leading economy after it rebased (updated the way it measures) its GDP.

But then global oil prices crashed, leaving the continent's most populous nation, which depends on crude export sales for 70 per cent of government revenue, desperately short of cash.

State sector salaries have gone unpaid, much-needed infrastructure projects shelved and the country's currency, the naira, has plummeted in value. Inflation has soared to above 17 per cent. Everything from fuel to food is more expensive.

After years of inaction and inept reaction from the previous government, President Muhammadu Buhari, who came to power in May 2015, has at least achieved successes in curbing Boko Haram's almost daily bloodshed.

But the years of conflict have taken their toll: rural northeast Nigeria — already desperately poor even before the insurgency — has been devastated: farmers have been killed or have fled; land for crops has not been sown or harvested for years.

The resulting food shortages have driven up prices in local markets, while the influx of the displaced to cities such as Maiduguri, the capital of Borno state, has heaped pressure on local authorities, leaving them struggling to cope.

Some 1.5 million people have sought safe haven in Maiduguri, more than doubling its population. Most have been taken in by friends and family or forced into overcrowded and unsanitary camps for the displaced.

A young child suffering from severe malnutrition lies on a bed in the ICU ward at the In-Patient Therapeutic Feeding Centre in the Gwangwe district of Maiduguri, the capital of Borno state, northeastern Nigeria, on Sept. 17, 2016. (Stefan Heunis/AFP/Getty Images)

The state and federal government response has been patchy: food such as rice and maize has reportedly been stolen and resold by corrupt officials; often it has not materialized at all.

There have been deaths in the camps from measles outbreaks and other preventable diseases because of low vaccination rates. During the current rainy season, typhoid, malaria and cholera are constant threats.

Host communities and volunteers have done what they can, even as the international aid effort has scaled up.

The American University of Nigeria, based in Yola, Adamawa state, has run feeding programs for the displaced for several years. In August it said it fed 75,000.

But AUN president Margee Ensign said the money to do so has now dried up — and those who previously returned to their homes in the countryside are coming back to the city in an even more desperate state.

"The problems related to famine, out-of-school children, lack of infrastructure are now far bigger," she told CBC News.

"We are seeing people come back to Yola malnourished and dying. There is a rapid increase in children on the streets."

A woman weak with hunger asked one AUN staff member to raise her one-week-old child. She later died. The employee took in the child, Ensign said.

Security officers are seen at the Bakkasi camp for internally displaced people, after security was called to control some refugees, who rallied against camp authorities for what they say is poor distribution of food rations, in Borno, Nigeria, August 29, 2016. (Afolabi Sotunde/Reuters)

The last time the world paid attention to Nigeria was after more than 200 schoolgirls were kidnapped from the remote town of Chibok, in Borno state, in April 2014.

The abduction sparked a huge online campaign — #BringBackOurGirls — featuring U.S. first lady Michelle Obama and Hollywood celebrities. But more than two years on, 217 of the 219 are still in captivity. UNICEF says some 7,000 children have been abducted.

Now, the images of Boko Haram are its child victims, those born into the conflict, starved to the brink of death by its consequences, leaving them little more than skin and bone or swollen by protein deficiency through lack of food.

Money is required — and fast — not just a hashtag.