“Next stop: Lagos!” Facebook CEO Mark Zuckerberg posted to his account in August 2016.

It was his first trip to sub-Saharan Africa and he was excited, he said.

Who wouldn't be? Some 53 million mobile internet users are forecast to come online in Nigeria over the next seven years: a lot for a company that partly measures its success on user growth.

When Zuckerberg touched down in Lagos, there were 16 million monthly Facebook users in Nigeria. Today, just two years later, there are 24 million.

But more users means more content, and a lot of that content, according to the police in Plateau State, is false, misleading, and dangerous.

Facebook is aware of the problem, and claims to be addressing it. “Nigeria is important to us,” said Akua Gyekye, the company’s public policy manager for Anglophone West Africa, in a recent statement. “We are committed to taking our responsibility seriously in tackling the spread of false news.”

Facebook told the BBC that it is pursuing a “multi-pronged approach” to combating the spread of misinformation in Nigeria. “As well as reports from our community, we’re using machine learning tools to help find and remove inappropriate content, are investing in local partnerships, and continue to engage with Nigerian civil society, NGOs, academics and policy makers.”

At the centre of Facebook’s efforts is a scheme that it calls the “third-party fact-checking programme”. The programme is part of a worldwide approach that Facebook has already rolled out in 17 other countries.

In Nigeria, the programme launched in October and the third parties are the French news agency AFP and the non-profit organisation Africa Check. Their fact checkers will review stories that have been picked up by Facebook’s automated system for detecting false information. The system includes posts that have been flagged as false or misleading by other Facebook users.

“We know there is no silver bullet,” said the Facebook spokesperson, Akua Gyekye, “but once a fact checker rates a piece of content as false, we are able to reduce its future views by an average of 80%”

The statistic sounds impressive. But BBC Africa Eye dug deeper into Facebook’s fact-checking initiative in Nigeria, talking to insiders and experts in the field. And when we got into the detail the picture looked rather different.

So far, Facebook’s third-party fact-checking partners, AFP and Africa Check, have committed just four people full-time in Nigeria to analysing and debunking false news, on a platform that is used by 24 million Nigerians every month.

Alexios Mantzarlis, director at the International Fact-Checking Network – the body that accredits fact-checking agencies – told us that an individual fact checker might be able to complete “between 20 and 100 individual fact checks” per month. But in Nigeria, where reliable public data is hard to find, the process is often slower. Another source working for one of Facebook’s fact-checking partners, who asked not to be named, said that fact checkers sometimes debunk just five stories in a week.

“They are just dipping their toes in the water,” said Gbenga Sesan, a Nigerian digital rights activist who has met Facebook representatives to discuss the company's expansion in Nigeria. “At the end of the day, these are business people and they want to make more money,” he said.

Julie Owono, the Cameroonian director of Internet Without Borders, a digital activist group, believes that Facebook’s plans are not commensurate with the scale of the problem. “There’s a dis-proportionality between the threat and the effort put in place,” she said. “Four fact checkers?... It’s scary.”

More worrying still is that none of the four fact-checkers deployed full-time by Facebook’s partners in Nigeria speaks Hausa, a language spoken by millions in the country.

Facebook told the BBC that their Nigerian fact checking partners “support Hausa.” The company later clarified this means the fact-checking teams can receive support from Hausa speakers in their network when required.

The BBC analysed more than 50 recent posts written in Hausa that contain hate speech or false information – and some of them are horrifying.

One post, for example, contains a photo of a person slumped on the ground, their skin burnt and peeling. The Hausa text reads: “This is John Okafor [an Igbo name] who tried to smoke weed using pages from the Qur’an and got burnt, instantly.”

In fact, the photograph was taken after a horrific assault on a woman accused of witchcraft in Lagos in 2014. She was reportedly burned alive and later died of her wounds.

But the facts didn’t matter to the person who created this post, and didn’t register with the people who liked it. What they saw was a story about a Christian – an ethnically Igbo Christian – displaying contempt for Islam, the predominant faith of Hausa-speaking Nigerians. It is the kind of story that, in a region already torn by ethnic and religious violence, can have dangerous consequences.