Built in 1982 on the outskirts of the capital Libreville, the facility was supposed to serve as a model for a continent where modern psychiatric treatment is in its infancy.
Now it seems more like a horror museum than a hospital.
"National Centre for Mental Health in Melen (CNSM)" reads a sign at the yawning gates of the facility.
Nobody watches over the premises or the several dozen patients -- 24 of them veteran "residents" -- who wander at will between their wards and the shops and school of a largely abandoned district.
Patients at the dilapidated CNSM have been left by families who could no longer cope or were picked up on the streets in a country that has just four qualified psychiatrists for a population of some 1.8 million.
They help in the public sector but earn their living largely in private practice, like colleagues elsewhere in Africa.
The CNSM still boasts a handful of administrative staff and three cooks are employed to cater for patients -- but they pass food from the kitchen between solid iron bars.
"Since they no longer get their medication, we're frightened of being attacked," a cook told AFP.
Rubbish piles up in filthy corridors and medical records lie where they were dropped along with other paperwork in buildings left to decay.
"We're treated like animals," said an unshaven man in rags before shuffling back into a bedroom.
'People are left to rot'
Mental illness attracts stigma widely in Africa, according to a 2013 report by Mary Amuyunzu-Nyamongo, executive director of the African Institute for Health and Development (AIHD) based in Kenya.
"A study conducted in Uganda revealed that the term 'depression' is not culturally acceptable amongst the population, while another study conducted in Nigeria found that people responded with fear, avoidance and anger to those who were observed to have a mental illness," the report said.
Beyond a door left ajar, a half-naked old woman lay prone on an iron bed staring wide-eyed at the wall. Her scalp was plastered with sores and the floor covered with urine and excrement in an appalling stench. Asked how she felt, she moaned.
"People are left to rot," protested Gael Koumba Ayoune, who heads the Rally of Young Gabonese Patriots, a movement formed last year to represent youth from poor districts ahead of 2016 elections.
In April a patient died in agony on the floor with nobody coming to his aid, although the psychiatric facility is officially part of the region's general hospital, with a full complement of medical services.
"He died in front of us," Ayoune said, adding that he had filed a negligence suit against the state.
"The state no longer meets the most basic needs of the population... Since he is presumed to be insane or elderly, a patient is no longer considered to be a human being," added the activist, whose association is extending the geriatric wing, opposite the psychiatric hospital.
The lack of resources is evident even in death. "There's no refrigerated morgue," Ayoune said. "When an elderly person dies, the body may lie for 24 hours in the dormitory with the others until the undertakers come."
'Cash flow problems'
Such difficulties are nothing new at the CNSM, whose staff have been on strike for more than two years to press for better working conditions.
According to the UN World Health Organisation, less than one percent of Gabon's national health budget is allocated to mental care. Yet mental disorders account for five percent of illness in sub-Saharan Africa, WHO figures show.
In a vicious circle, poverty renders those who could never hope to consult a specialist vulnerable to mental illness, while people already sick face further impoverishment because of their inability to function normally.
Serges Mikala, the secretary general of the National Union of Health Personnel (SYNAPS), said the Melen complex had been badly run and that he suspected that money intended to fund it had been "given over to other things".
"We urgently need to repair the building used for the most violent patients, install restraints, and provide vehicles for fieldwork and medicines," he declared.
Apart from mental disorders, patients suffer from "numerous other problems of AIDS and malaria, which we lack the means to treat," Mikala added.
"Today, there's no longer a strike because that's become the status quo. We ask how the hospital can start working again with a fictitious operating budget, because there's no more money."
At the ministry of health and social welfare, officials acknowledged "cash flow problems" due to an economic crisis fuelled by a drop in prices for its oil exports.
"Mental health is of concern to Gabonese authorities at the highest level," senior ministry official Leonard Assongo said, announcing a second "emergency plan" in three years and expecting work at Melen to resume "between now and the month of June".