A total of 75% of registered voters who participated in the Zimbabwe's tightly-contested elections yesterday, show that top presidential contenders - Emmerson Mnangagwa (Zanu PF) and Nelson Chamisa (MDC Alliance) - are reportedly in a neck-to-neck race, with the first batch of results expected this morning.
"Awaiting ZEC to perform their constitutional duty to officially announce the people's election results and we are ready to form the next government", said Chamisa, who is vying to become Zimbabwe's youngest head of state, on his official Twitter feed.
As well as voting to elect a president, Zimbabweans voted for 210 members of parliament and more than 9,000 councillors.
Deposed president Mugabe, who ruled Zimbabwe for 37 years, voted in Highfield, Harare.
Mugabe defended Zimbabwe's election commission after Chamisa and the opposition raised concerns that the vote will be flawed, saying that "it acts quite freely".
"The people's will being negated & undetermined due to these deliberate & unnecessary delays", Chamisa tweeted.
The ZEC was not immediately available to comment.
Previous polls have been marred by allegations of widespread rigging and intimidation. Observers said they had seen few problems other than some poor organisation in places.
Elmar Brok said many voters, particularly young women, had left voting queues in frustration at long delays, and that his mission had not yet reached a conclusion on how to judge the vote.
Later on Sunday, Mnangagwa said in a video posted on Facebook that Chamisa had "forged a deal" with Mugabe and that a vote for the opposition leader amounted to an endorsement of the old order.
A run-off vote is scheduled for September 8 if no presidential candidate wins at least 50%.
A record of more than 20 presidential candidates and almost 130 political parties were participating.
Has promised to rebuild the country's devastated economy, but has been criticised for making extravagant promises - such as the introduction of a high-speed bullet train and bringing the Olympics to Zimbabwe.
"However the public's faith in the secrecy of the ballot is essential for the credibility of the process".
With hours ticking towards Zimbabwe's harmonised elections tomorrow, President Emmerson Mnangagwa has implored Zimbabweans to maintain the peace and non-violence that have characterised the campaign period.
Pastor Evan Mawarire, who rose to prominence in 2016 by rallying support against Mr Mugabe's government on social media, failed in his attempt to win a seat on Harare's city council.
Former president Robert Mugabe, 94, cast his vote in a Harare township on Monday in Zimbabwe's first election that does not include his name on the ballot paper.
"I am very happy that the process for campaigning was peaceful [and] voting today is peaceful", he said.
Long lines formed outside many polling stations in Harare, the capital, and elsewhere.
Mugabe had ruled the country since gaining independence from Britain in 1980.
But he has lived in obscurity since he stepped down under military pressure in November.
The election could confirm the country's rehabilitation after years as a pariah under Mr Mugabe and help unlock foreign investment, especially if Western observers, monitoring for the first time since 2002, declare it fair.