Three decades after he first came to power in a military coup, Muhammadu Buhari will be sworn in on Friday as elected President of Nigeria, giving him control of an African giant struggling with slowing economic growth and a raging Islamist insurgency.

Despite the problems facing Africa's most populous nation and biggest oil producer, Buhari's historic election victory - Nigeria's first democratic transfer of power - has inspired hope for a new sense of direction and purpose after five years of scandal and drift under outgoing President Goodluck Jonathan.

"It's not so much that people love Buhari. But they were tired of this stagnation, this lack of movement, this seeming cluelessness of administration," said political analyst Ebun-Olu Adegboruwa.

A sandal-wearing ascetic from Nigeria's predominantly Muslim north, Buhari has already pledged to get tough on the corruption that pervades every aspect of life in Africa's biggest economy.

Although his roots are in the military, not economics, he served as head of the Petroleum Trust Fund under Sani Abacha, another military ruler, giving him insight into the murky world of crude oil production.

During Jonathan's time in office, the state oil company, NNPC, was accused by the central bank governor of failing to remit up to $20 billion in oil revenues to the government - an allegation that cost the respected banker his job.

Buhari has also vowed to spare no effort to defeat the Islamist Boko Haram militants who have killed thousands and displaced more than a million people in a six-year campaign to establish a caliphate in the northeast region abutting Lake Chad.

Befitting Buhari's modest personal and political style, there was little fanfare in the capital ahead of the swearing in, with security checkpoints leading to Abuja's Eagle Square and a few green and white national flags lining the main expressway.

About 30 countries have sent high-level representatives for the ceremony, many from the rest of Africa, which stands to gain if Buhari is able to breathe new life into the economy and restore Abuja's diplomatic credibility and clout.

South African President Jacob Zuma will be there, a sign of Pretoria's desire to improve relations with Abuja after a series of diplomatic spats under Jonathan, including the deaths of 84 South Africans in a Lagos church building collapse in September, and a wave of attacks on foreigners in South Africa this year.

U.S. Secretary of State John Kerry, British foreign secretary Philip Hammond and French foreign minister Laurent Fabius were also flying in.