Ivory Coast's President Alassane Ouattara has secured a fourth term following an election in which two of his biggest challengers were barred from running, provisional results show.

Ouattara, 83, won 89.8% of the vote, the electoral commission said on Monday, and businessman Jeal-Louis Billon came a distant second with only 3.09%.

The landslide victory is not a huge surprise, as after being banned from the presidential race, former President Laurent Gbagbo and Credit Suisse ex-CEO Tidjane Thiam had urged their supporters to boycott the vote.

Voter turnout reached just 50.1%, according to the electoral commission.

Gbagbo's ex-wife, Simone Gbagbo, who was allowed to contest the election, got 2.42% of the vote.

Monday's results are provisional, and the outcome will be announced by the Constitutional Council after it rules on any election petitions.

On Sunday, the opposition group made up of Gbagbo and Thiam's parties denounced the election as a "civilian coup d'etat," saying they would not recognise Ouattara as a validly elected leader.

Ouattara first assumed the presidency in 2011, following Laurent Gbagbo's arrest after his refusal to accept defeat in the 2010 election.

Ouattara was originally restricted to serving two terms, but a 2016 constitutional overhaul allowed him to seek re-election in 2020, in a vote that was boycotted by the opposition.