Nigerian tops list of Africa's billionaires

There are far more African billionaires than previously thought, according to a report on the continent's mega-rich, but the number of Africans living in extreme poverty has also shot up.

Previous Africa rich lists have named as few as 16 billionaires but pan-African business magazine Ventures said it had identified at least 55 on a continent where the wealthy often fiercely protect details about their fortunes.

Of the 55, 20 are Nigerian, including several oil barons, while South Africa and Egypt have nine and eight, respectively.

Ventures supported reports by Forbes, which listed Nigeria's Aliko Dangote as Africa's richest man with a fortune of $US20 billion ($21 billion).

Mr Dangote, who made his fortune in cement, heads a multi-interest empire, profiting from products including flour and sugar, while eyeing a massive investment in oil refining.

The continent's richest woman is Nigeria's Folorunsho Alakija, whose Fama Oil owns an offshore oil block, which she acquired in 1993 "at a relatively inexpensive price", likely through a helpful connection.

The most prominent South African named is Nicky Oppenheimer, worth an estimated $US6.5 billion, whose fortune came largely from the diamond mines his family controlled for decades, which were operated by De Beers.

He sold his family's stake in De Beers two years ago.

The figure of 55 is "an under-estimate", Ventures founder Chi-Chi Okonjo said.

Corruption is rife on the continent and the rule of law still unevenly applied. African business moguls often face accusations that their fortunes were illegitimately earned, including with help from political patrons.

The apparently rising number of ultra-rich Africans has come amid broader economic growth on the continent, with an average of 5 per cent gross domestic product expansion since 2010.

But economic growth has not kept up with a rising population.

"There are more than twice as many extremely poor people living in sub-Saharan Africa today (414 million) than there were three decades ago (205 million)," the World Bank said in April.

It is the only region where "the number of poor people has risen steadily and dramatically" over the last 30 years, the bank said.