Mozambique's incumbent President Filipe Nyusi has won 73 percent of the vote in a presidential election, the National Election Commission (CNE) said, securing a landslide victory in a contest opposition parties say was marred by fraud and violence. 

Ossufo Momade, the candidate for the main opposition party and former guerrilla movement Renamo, trailed behind with 21.88 percent of the vote, Commission Chairman Abdul Carimo said at a news conference on Sunday. 

During his second five-year term, Nyusi, of the ruling Frelimo party, will be responsible for overseeing a gas boom led by oil giants such as Exxon Mobil Corp and Total, battling an Islamist insurgency and delivering on a peace deal signed two months ago. 

It was hoped the October 15 presidential, legislative and provincial poll could set the seal on the fragile deal, designed to put a definitive end to four decades of violence between Frelimo and Renamo, but instead the pact is at risk of falling apart as opposition parties reject the results. 

Frelimo says the elections were free and fair. Nyusi was widely expected to triumph but not by such a large margin. 

Daviz Simango, of the third largest party the Mozambique Democratic Movement, secured just over 4 percent of the vote, with less than 1 percent going to Mario Albino, who heads up smaller party AMUSI, according to the CNE. 

Simango said earlier on Sunday that MDM sees the election outcome as "null and void," and demanded an audit of the process that it said was tarnished after electoral administration bodies manipulated the process from the outset. 

Renamo has also already rejected the outcome after estimations based on numbers posted outside polling stations predicted a big win for Nyusi and Frelimo.