Mozambique's incumbent President Filipe Nyusi has taken an early lead in results from this week's presidential election but the main opposition party has questioned the results, stoking tensions just two months after a peace accord.

With around 39% of the votes counted from roughly 13 million registered voters, Nyusi has taken a lead securing 68.85%, while his main competitor Osuffo Momade of the Renamo party has racked up 26.20% of the vote so far.

The secretary general of Renamo, Andre Magibire, said the party was unhappy with the way Tuesday's presidential, legislative and provincial elections were carried out and that there had been ‘massive fraud’.

The party held a press conference on Saturday and issued a statement accusing Frelimo of violating the country's fragile peace accord.

The poll was seen as make or break for the peace pact, which put a formal end to decades of hostility between Renamo and Frelimo.

The two fought on opposite sides of a civil war that ended in a truce in 1992, but have clashed sporadically in the years since.

Magibire said Renamo would hold a meeting on Monday to decide its next steps.

After casting his vote, Momade warned Nyusi not to manipulate the election results and said his party could not accept the outcome if it were rigged.

Frelimo's spokesman Caifadine Manasse said elections were fair, free and transparent and would not affect the peace agreement.