Tinubu inherits a struggling economy with record debt, shortages of foreign exchange and fuel, a weak naira currency, nearly two-decades-high inflation, skeletal power supplies and falling oil production due to crude theft and underinvestment.

Protectionist policies and foreign currency interventions under predecessor Muhammadu Buhari spooked investors.

"On the economy, we target a higher GDP growth and to significantly reduce unemployment," he said, adding that this would be achieved through budgetary reform, boosting power generation and improving food security.

"I have a message for our investors, local and foreign: our government shall review all their complaints about multiple taxation and various anti-investment inhibitions."

Tinubu took his oath in an open-air ceremony in the capital's Eagle's Square. Buhari departed to his rural home in northern Katsina state afterwards.

The former Lagos state governor and member of Buhari's party said a popular but costly fuel subsidy would be gone in line with this year's budget that set its removal from June.

He also promised "thorough house cleaning" of monetary policy, adding that the central bank should work towards a unified exchange rate.

"This will direct funds away from arbitrage into meaningful investment in the plants, equipment and jobs that power the real economy," he said.

'EXTEND MY HAND'

Tinubu also inherits a divided country after his disputed victory that is being challenged in court by his main rivals who see him as a member of the old guard.

But Tinubu said his electoral victory was fair.

"My supporters, I thank you. To those who voted otherwise, I extend my hand across the political divide. I ask you to grasp it in national affinity and brotherhood," he said.

The February election had galvanised young voters hoping for a break from the two parties that have dominated Nigerian politics since military rule ended in 1999. But what authorities promised would be the freest and fairest election yet ended in frustration for many.

Tinubu said he would tackle widespread violence in Nigeria by reforming the security services with more personnel and improved training, equipment and pay.

Buhari has touted successes in a 13-year fight against Islamist insurgents in the northeast, where his government ramped up military spending.

But insecurity has spread. Killings and kidnappings for ransom are rampant in the northwest. Separatist and gang violence plague the southeast, and clashes between farmers and herders persist in hinterland states known as Nigeria's Middle Belt.