A former governor has been elected head of Nigeria's Senate, becoming the third most powerful person in the country by challenging the wishes of the presidential coalition to which he belongs.

Bukola Saraki's victory highlights the cracks appearing in the coalition that brought President Muhammadu Buhari to power.

Party officials say Buhari was meeting with his party's senators about a consensus candidate when Saraki pushed the vote through.

Saraki defected from former President Goodluck Jonathan's party to Buhari's coalition last year but got Tuesday's votes from the opposition. It could be a sign Jonathan's party is gaining power to undermine Buhari just days after his May 29 inauguration.

Saraki was a two-term governor of Kwara state best known abroad for importing white Zimbabweans to develop agriculture.