At least one person was killed in Zimbabwe's capital Harare on Wednesday as soldiers stepped in to disperse stone-throwing opposition supporters who accused the ruling party of trying to rig Monday's presidential election, witnesses said.
The ruling ZANU-PF party won a majority of seats in Parliament, the electoral commission said.
Observers from the European Union said that while the election marked a clear break from the past, "a truly level playing field was not achieved".
The House of Assembly of Parliament has 210 seats and Zanu PF would need to win 30 more to have a two-thirds majority that would allow it to change the constitution at will.
"We requested for the assistance of Zimbabwe Defence Forces (ZDF) for the suppressing of the commotion and disturbances in Harare central business district".
The riots surged up to the fence of the Rainbow Towers Hotel & and Conference Centre, where the electoral commission has been announcing results and many global election observers are staying.
"I am not happy because at the polling station where I voted most of the people were voting for MDC alliance but if you see the results of the constituency it does not reflect the will of the people".
Harare was tense as people waited to find out the victor of the presidential election, and about 150 opposition supporters gathered outside the hotel where results are being released.
A man has been shot dead in the clashes between armed police operatives and protesters of the the opposition, Movement for Democratic Change (MDC) alliance.
The results of the presidential election, which is a separate contest pitting Mr Mnangagwa against Mr Chamisa, are yet to be declared, but the parliamentary results bode well for the incumbent.
"Equally, we hold the party and its leadership responsible for any loss of life, injury or damage to property that arise from these acts of political violence which they have aided and abetted". "So I have yet to learn why they will be released last", he added, urging the electoral commission to release the results as fast as possible and for each individual polling station.
African observer groups said the vote was peaceful, orderly and largely in line with the law but they raised concerns about bias of state media and the commission.
But just hours later, President Mnangagwa said he was "positive" of the election outcome in Zanu PF's favour.
As Zimbabwe awaits the final result of the presidential election, both the MCD Alliance and ZANU-PF are confident of success.
For now at least, Zimbabwe appears set to traverse a long and hard path if it is to regain its reputation as one of Africa's most promising economies.
Its population of 13 million is struggling amid shortages of foreign currency, unemployment above 80% and lack of foreign investment.
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