Africa's wealthiest man, Aliko Dangote, says he aims to invest up to $8bn in a major new oil refinery that would almost double Nigeria's oil output.Nigeria is Africa's biggest oil producer but lacks refining capacity and has to import most of its fuel.Mr Dangote, 56, told Reuters news agency that those who should have invested in refineries were benefiting from Nigeria's lack of capacity.Building a major refinery would help all of sub-Saharan Africa, he said.The tycoon, who made his fortune in cement, flour and sugar, is worth an estimated $16bn (£10bn; 12bn euros) and has topped the Forbes list of Africa's richest men for the past three years.Work on constructing the refinery would begin this year and it would eventually have the capacity to produce 450,000 barrels per day, he said.He stressed that a new refinery was vital for Nigeria: "It has to be done.""In five years, when our population is over 200 million, we won't have the infrastructure to receive the amount of fuel we use."The BBC's Will Ross in Lagos says it is a scandal that Nigeria has to import more than three-quarters of its fuel despite being the continent's biggest producer.Although it has two refineries in the Port Harcourt area, neither runs at full capacity.Previous efforts to repair Nigeria's dilapidated refineries and build new ones have been scuppered to protect the interests of powerful fuel importers, some of whom have been linked to a subsidy scam costing the country billions of dollars a year, our correspondent adds.Fuel in Nigeria is sold at a subsidised price. A government attempt to remove the subsidy in 2012 led to nationwide protests. The plan was subsequently dropped.Last year an investigation revealed that in two years, over $6bn was lost in a fuel subsidy scam.The inquiry into the subsidy scam was then set up but the legislator leading it was later arrested over bribery allegations.Mr Dangote acknowledged in his interview that his refinery plan may face opposition."The people who were supposed to invest in refineries, who understand the market, are benefiting from there being no refineries because of the fuel import business," he said.