If Chamisa disputes the result or no one candidate gets more than 50 percent and there is a runoff, there are fears of street protests and possible violence.
Both Chamisa and Mnangagwa have vowed to rebuild an economy shattered by Robert Mugabe's long rule.
Mugabe said he was forced to resign last November at a time he had already planned to voluntarily step down at Zanu-PF's congress the following month and hand-over power to former defence minister Sydney Sekeramayi.
Mnangagwa, 75, who promises a fresh start for the country despite being from the ZANU-PF elite, is the front-runner with the advantage of covert military support, a loyal state media and a ruling party that controls government resources. During the address, he also addresses rumors that he planned to have his wife, Grace Mugabe take over, calling them "utter nonsense".
"I said I can't vote for those who have caused me to be in this situation.so there is Chamisa left".More news: Trump Denies Knowing About 2016 Russian Lawyer Meeting
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He said he would rather make a choice among the 22 presidential candidates vying for election‚ but went on to hint that those candidates‚ who had not made an impact in rallies‚ were not worth his vote. "He seems to be doing well going by his rallies‚" he said.
"Our neighbours are fooled to believe to believing that it was not a coup d'etat".
Many in Zimbabwe knew no other leader but Mugabe, who led the country for 37 years and since independence from white minority rule in 1980. "I say no, no, no". He denied accusations he had used the army to suppress dissent.
He said a lot of Zimbabweans were afraid and they were sending him messages to say so.
Mr Charisma has accused the incumbent party of dirty tactics as well as the Zimbabwe Electoral Commission of bias towards ZANU-PF.
Mugabe described tomorrow's voting day as "the greatest event" which he hopes will bring back "constitutionalism from a military government". But him and any other persons in his alliance, I have not met.