Ghana's electoral commission on Monday declared ex-president and main opposition leader John Dramani Mahama winner of Saturday's presidential election with 56.55% of the vote, according to provisional results.

Mahama's main rival, vice president and ruling-party presidential candidate Mahamudu Bawumia, already conceded defeat on Sunday in both presidential and legislative elections to ease tensions.

The electoral commission said it had counted votes from 267 out of the West African country's 276 constituencies. Voter turnout was 60.9%.

Mahama, 66, is making a comeback after serving as Ghana's president from 2012 to 2016. He described Bawumia as representing a continuation of the policies that led to Ghana's worst economic crisis in a generation.

"This mandate serves as a constant reminder of what fate awaits us if we fail to reach the aspirations of our people and govern with arrogance," he told hundreds of jubilant supporters at his campaign grounds after results were announced.

"The victory shows that the Ghanaian people have little tolerance for bad governance," he added, promising "severe measures and governance reforms" to "reset our nation".

In an interview with Reuters before the election, Mahama said he would seek to renegotiate terms of a $3-billion International Monetary Fund bailout secured last year to restructure the country's debt.

He has also promised to ease business regulations, introduce a 24-hour triple-shift work system, enact tax reforms and invest $10-billion in modernising infrastructure.

A spiralling economic and cost-of-living crisis in Ghana, which produces cocoa, gold and oil, hit the popularity of Akufo-Addo's government and increased momentum for a change in leadership.