Zimbabwe's main opposition presidential candidate Nelson Chamisa has said he was confident of victory, despite the "machinations and shenanigans" of the electoral commission to help President Emmerson Mnangagwa and his Zanu-PF party to stay in power.

Zimbabwe's electoral commission was biased, and it had "thrown away the whistle" to join Mr Mnangagwa's team, Mr Chamisa added.

"We will defeat the referee and player. We will not allow them to get away with murder, literally and metaphorically," he said at a press conference.

The electoral commission was "stubborn and "arrogant" and had violated the law in its preparations for Monday's poll.

The commission had, for instance, failed to disclose how many ballot papers had been printed, and what measures had been taken to ensure they were secure, Mr Chamisa said.

The opposition would not accept a "fake" result, but was confident of winning even with "our hands tied at the back", Mr Chamisa said.