Gunfire crackled in the streets while troops, backed by armoured vehicles and a military helicopter and some with their faces masked, cleared the streets.
One person was shot dead near a bus rank, witnesses at the scene told a Reuters photographer.
The deployment of soldiers and their beating of unarmed protesters is a setback to President Emmerson Mnangagwa`s efforts to shed Zimbabwe`s pariah status after decades of repression under Robert Mugabe, who was ousted in a coup in November.
Even before the violence, European Union observers questioned the conduct of the presidential and parliamentary poll, the first since Mugabe`s forced resignation after nearly 40 years in charge of the Southern African nation.
The violence started soon after opposition Movement for Democratic Change (MDC) leader Nelson Chamisa claimed he had won the popular vote.
Scores of his supporters who had been burning tyres in the streets then attacked riot police near the Zimbabwe Election Commision (ZEC) headquarters. Officers responded with tear gas and water-cannon.
"I was making a peaceful protest. I was beaten by soldiers," said Norest Kemvo, who had gashes to his face and right hand.
Justice Minister Ziyambi Ziyambi said the army had been called in to ensure "peace and tranquility".
Without the stamp of approval of the international community, Zimbabwe`s next leader will struggle to unlock the billions of dollars of international donor finance needed to get the shattered economy back on its feet.
The EU observers expressed concern about delays in releasing the results of the presidential contest, a two-horse race between Chamisa and Mnangagwa, head of the ruling ZANU-PF party.
As gunfire echoed through downtown Harare, Mnangagwa called for calm and urge patience while results were collated.
The electoral commission had said it would start announcing results for the presidential race from 10.30 GMT but that was then pushed back at least 24 hours.
With three seats yet to be declared in the parliamentary contest, ZANU-PF had 144 seats compared to 61 for the MDC, meaning the ruling party achieved the two-thirds majority that permits it to change the constitution at will.
Chamisa said the early release of the parliamentary results was a deliberate ploy to prepare Zimbabweans for a victory by Mnangagwa, a former national security chief nicknamed `The Crocodile` and commonly referred to by the initials ED.
"The strategy is meant to prepare Zimbabwe mentally to accept fake presidential results. We`ve more votes than ED. We won the popular vote (and) will defend it," Chamisa said on Twitter.
Before the violence, EU Chief Observer Elmar Brok said he did not yet know if the shortcomings would have a material effect on the outcome of the vote, but criticised the electoral commission for being at times "one-sided".
The EU`s assessment is critical in determining whether Zimbabwe can repair its image and attract the foreign investors needed for an economic revival.
The EU did not understand why the release of the presidential result was taking so long, Brok said.
"The longer it lasts that the results of the presidential election is not known, the more lack of credibility it provides," he said.
Zimbabwe was once one of Africa`s most promising economies but became descended into corruption, mismanagement and diplomatic isolation in the latter stages of Mugabe`s administration.
Its population of 13 million is struggling amid shortages of foreign currency, unemployment above 80 percent and lack of foreign investment.
(U.Goo5)
(Uu.SYS/C/G005/C/C003) 02-08-2018 07:19:00
Reporter: Antara/Reuters
Editor: Fardah Assegaf
Copyright © ANTARA 2018
