The government late Wednesday vowed to enforce a security crackdown to prevent further unrest after the army opened fire to disperse opposition protests in Harare, leaving at least three people dead.
Zimbabwean president and leader of the ruling Zimbabwe African National Union - Patriotic Front (ZANU-PF) Emmerson Mnangagwa, one of the 23 candidates on the presidential ballot, blamed the opposition for inciting violence in order "to disrupt electoral process".
MDC supporters, who say their leader Nelson Chamisa won the vote, burnt tyres and pulled down street signs as protests spread from the party headquarters in Harare.
Zimbabwe's electoral commission has said the results of the presidential election will be announced "very soon", while a new joint statement by worldwide election observer missions urges the quick release of those results.
The EU mission questioned why presidential votes were counted first but were being announced last.
On Thursday, the United Nations called on both sides to "exercise restraint" following the landmark polls that saw the ruling ZANU-PF party winning a majority of seats in parliament.
Writing on Twitter, Mr Mnangagwa also called for an independent investigation into the violence, in which three people were killed after soldiers were deployed to the streets of the capital.
A credible vote is crucial to the lifting of global sanctions imposed on Zimbabwe so that its collapsed economy can recover.
Opposition leader Chamisa accused the ZANU-PF of trying to steal the election after official figures gave it a two-thirds majority in parliament.
It said that by using live ammunition against unarmed protesters, "the army has broken the very same rule of law that they should protect".
Hard-line cleric, speaker vote in Pakistan
Khan's camp was increasingly confident, but it still appeared likely to fall short of a clear majority in the National Assembly. For the first time in 2013, a civilian government in Pakistan completed its five-year term.
Police patrol outside the Zimbabwe Electoral Commission offices as opposition supporters gather, in Harare, Zimbabwe, on August 1, 2018.
ZEC was expected to announce more results early this morning.
The much-criticised election authority meanwhile declares there has been no rigging, after the opposition repeatedly alleges the vote process was flawed.
A wounded man takes shelter in a market stall in Harare as protests turned violent.
African observer groups said the vote was peaceful, orderly and largely in line with the law but raised concerns about bias of state media and the commission.
The ruling party forced Mugabe to resign in November, when the military briefly seized control of the country, and replaced him with Mnangagwa, his former deputy and spy chief.
Under Mugabe, elections were often marred by fraud and deadly violence.
Races in some constituencies were so close that they could have gone to the opposition Movement for Democratic Change (MDC), had it not been split between Nelson Chinamasa's MDC Alliance and Thokozani Khupe's MDC-T.
In Harare, the contrast could not be starker with November, when hundreds of thousands filled the streets, hugging soldiers and celebrating their role in ousting 94-year-old Mugabe, the only leader Zimbabwe had known since independence in 1980.
In an indication of the growing tension, a crowd of about 100 MDC supporters gathered outside a Harare hotel where election results were being announced but police blocked the entrance to the building, a Reuters witness said.