Soldiers are circulating in Harare, telling vendors and other people to leave the city centre by noon.
On Wednesday afternoon, riot police were stationed outside the electoral commission in the capital, Harare, where a crowd of opposition supporters gathered to await the results. "So far, it shows that the people of Zimbabwe have entrusted ZANU-PF to lead them and we will do our best to meet the people's wishes in the constituencies that elected us". "Are we at war?"
The opposition says it condemns violence in all its forms.
Zimbabwean soldiers have shot a person dead on the streets of Harare.
Supporters of the Movement for Democratic Change, Zimbabwe's primary opposition party, protest against alleged fraud by the election authority and ruling party Wednesday in Harare.
Observers say it could be a tight race, but the opposition has said it will protest if their candidate is defeated.
The electoral commission had warned that final results of the presidential first round may not be known until Friday or even Saturday. The result in the presidential vote is due by 4 August but expected sooner.
The opposition alleges the vote was rigged.
The election, the first since the military ousted Mr. Mugabe in November and installed his former deputy and ally, has been seen as a major test of Zimbabwe's democracy and its ability to hold a free and fair election.
With three seats yet to be declared, Zanu-PF had 144 seats compared to 61 for the MDC, meaning the ruling party achieved a two-thirds majority which would allow it to change the Constitution at will. "No amount of results manipulation will alter your will", he tweeted before the army was deployed on Wednesday.
He added: "The strategy is meant to prepare [Zimbabwe] mentally to accept fake presidential results". We have won the popular vote.
"We categorically denounce the excessive use of force against unarmed civilians", former Ghanaian president John Mahama said in a statement on behalf of the Commonwealth.
"There is a deliberate delay in formally announcing results", he told a news conference, characterising it as "interference with the people's will".
A presidential candidate needs more than half of the votes to claim victory. They believe the election has been stolen, and are demanding the MDC be announced as victor. Inside the main gate, a water cannon mounted on a police vehicle blasted protesters who hurled rocks that bounced off its armored plating.
UN Secretary General Antonio Guterres urged Zimbabwe's politicians to exercise restraint, while United Kingdom foreign office minister Harriett Baldwin said she was "deeply concerned" by the violence.
Home Affairs Minister Obert Mpofu said those who violated election rules by prematurely declaring victory risked incurring the "wrath of the law". Its population of 13 million is struggling amid shortages of foreign currency, unemployment above 80 percent and lack of foreign investment.
The case is different outside the ruling party headquarters, as there was no sign of supporters or heavy presence of security agents. "We had to consult among ourselves whether it would be safe", said one worker who declined to give his name.