Having lived for exactly half his life under a bridge in Nigeria’s biggest city, Lagos, Liya’u Sa’adu sees himself as the “guardian” for the many other homeless people who have joined him there.

More than 60 men now live in the tightly knit outdoor community – with the busy and noisy Obalende Bridge over them – as renting even a shack has proved unaffordable for them.

Mr Sa’adu advises the newcomers – often young people from far-away towns and villages – on how to be streetwise in fast-paced Lagos, where it is easy to fall into crime and drugs.

“I am 60 and there are young people who came here a few months ago or a few years ago. I see it as my responsibility to guide them,” he tells the BBC.

“It is so easy to lose track here in Lagos, especially for young people because there is no family to watch their steps.”

Like most of those who live under the bridge, he speaks Hausa, the most widely spoken language in the north of Nigeria.

He arrived here from the small town of Zurmi in north-western Zamfara state in 1994 – but all those he made friends with then have either died or have moved back to their hometowns or villages.

Tukur Garba, who began living under the bridge five years ago, says Mr Sa’adu’s advice has been invaluable and he commands huge respect from those who arrive to try their luck in Nigeria’s economic hub.

The 31-year-old hails down from the far northern state of Katsina, about 1,000km (621 miles) away.

“He is like our elder brother because he has been here for so long. We do need words of wisdom from him because it is easy to get in trouble in Lagos,” he says.

The area has now been dubbed “Karkashin Gada”, which in the Hausa language means “Under the Bridge”.

“The people who come here know someone who is already staying here or have a contact who told them about Karkashin Gada,” Mr Sa’adu says.

“When I came here, there were less than 10 people.”

Adamu Sahara, who has lived in an apartment close to Karkashin Gada for more than 30 years, says that homelessness is increasing in Lagos.

“Insecurity [including an insurgency by jihadist groups] and the failing economy has made a lot of people to flee northern Nigeria,” Mr Sahara says.

“Nigerian leaders have to be aware of what is happening so they can fix the problem because no human being is supposed to sleep under a bridge.”

Karkashin Gada’s longest resident has no plans to return to Zamfara as economic opportunities there remain bleak with kidnapping and banditry on the rise.

This has forced many people to abandon their businesses and farms as they risk being taken hostage by gangs demanding ransom payments.

To make life as comfortable as possible, Mr Sa’adu has acquired a mattress, some bedding, a wooden cabinet and a mosquito net.

He has put the mattress on top of the cabinet, and that is where he sleeps.

Mr Sa’adu is among the better-off as some of the other men who live there have no furniture, and share sleeping mats which they roll out on the floor.

Thankfully the risk of theft is minimal as some “residents” of Karkashin Gada are usually around, either working or enjoying their time off.

They all use a nearby public bath and toilet at a cost of 100 naira ($0.06; £0.05) a visit.

Cooking – or lighting fires, even in winter – rarely happens in Karkashin Gada as most of its inhabitants buy food from vendors who sell dishes popular with northerners.

“This is one of the places in Lagos where you see a large number of people from northern Nigeria so I sell fura [millet flour mixed with fermented milk] here and I am happy to say a lot of people do buy,” food vendor Aisha Hadi tells the BBC.

During his three decades in Lagos, Mr Sa’adu has progressed from being a shoe-shiner to being a scrap-metal seller – picking up metal from the streets and workshops for a business that sells it on for recycling.

It earns him an average of 5,000 naira ($3; £2) a day, above the extreme poverty threshold of $1.90 a day but barely enough for him to survive.

“Don’t forget I have to also send money to my family back in Zamfara every week, so it is a continuous struggle,” Mr Sa’adu says.

It is unclear how many people sleep on Lagos’ streets, but non-governmental organisations say they are up to half-a-million.

In the last few months, the Karkashin Gada community has come under heavy pressure from the Lagos state environmental task force.

Its officers carry out occasional raids as they say people are living there illegally.

Those arrested risk fines of up to 20,000 naira ($12; £9), a week’s income for many of the people living under the bridge.

“They come at around 1am or 2am, to arrest people sleeping here. Where do they want us to go?” Mr Garba says, adding that by morning most “residents” will have returned.

He urges the government to show compassion, and “to look into the issue of housing so that poor people like us can get good places to live”.

But in Nigeria, the government does not provide shelter for homeless people. Nor is there any plan to do so.

Instead, the current focus in Lagos is on helping people on low salaries – such as cleaners, drivers and messengers in offices – to buy homes.

For people like Mr Sa’adu, any type of housing in Lagos is unaffordable – renting a shack in an informal settlement costs around 100,000 naira ($48; £62) a year, while in a working-class area, a small apartment costs around 350,000 naira ($220; £170) annually.

Worse still, many landlords demand a year’s rent at the time of occupation, with no plans by the government to regulate the market despite the fact that the cost-of-living crisis is making housing unaffordable for even some young professionals.

Against this backdrop, the likes of Mr Sa’adu have resigned themselves to continue living under Obalende Bridge.

“Considering what I do, it’s difficult to save enough to get a decent place to stay,” he says as he lies on his mattress with the noise of vehicles driving just above his head.

“I am already used to the sound of cars. It doesn’t affect my sleep at all especially after a tired day,” he adds.