Zimbabwe opposition party MDC moves to Constitutional Court to challenge last week’s presidential election results.
President Mnangagwa was declared winner of the elections with 50.8 per cent of the total votes cast to Mr Chamisa's 44.3 per cent.
MDC says it has sufficient evidence to reverse the outcome of the polls.
Zimbabwe opposition leader Nelson Chamisa has filed a petition challenging President Emmerson Mnangagwa’s July 30 election victory.
The Movement for Democratic Change (MDC) leader alleges electoral fraud and other malpractices during the historic polls, the first to held without former ruler Robert Mugabe.
MDC lawyer Thabani Mpofu said on Wednesday that the party had assembled a strong legal team to face off with the Zimbabwe Electoral Commission (ZEC).
“We are working with a huge team of local lawyers and internationally recognised constitutional lawyers on this petition,” he told journalists in Harare.
The opposition also accuses the army of launching a crackdown against its leadership and supporters in a bid to stop the court challenge.
“My team is being harassed but we do not fear them and we are happy to address the Constitutional Court whilst on death beds and in prison,” he said.
Earlier on Wednesday police arrested senior MDC official Tendai Biti at the border as he tried to flee to Zambia. Mr Biti had claimed victory for the party prior to ZEC's announcement of the presidential results, sparking protests which turned bloody when military opened fire, leaving six people dead.
'Overwhelming evidence'
On August 3, President Mnangagwa was declared winner of the elections with 50.8 per cent of the total votes cast to Mr Chamisa's 44.3 per cent.
But Mr Chamisa dismissed the outcome terming it "unverified fake results."
Mr Mpofu said his team has sufficient evidence to reverse the outcome of the polls.
“The evidence is not only overwhelming, it’s also embarrassing (against ZEC),” he added.
The ruling party Zanu-PF said it has picked a team of 12 lawyers for the case filed by Mr Chamisa.
Under Zimbabwe’s electoral laws, the Constitutional Court must hear and conclude the election petition within 14 days.
President Mnangagwa, who succeeded Mugabe after he was ousted last November, will have to wait for the verdict of the court to know whether he will be sworn-in or not.
His inauguration had been scheduled for August 12.