The MDC's Chris Mbanga was unsure how long the consultation would last
Zimbabwe's Electoral Commission has started to verify the results of the disputed presidential election, more than five weeks after the vote.
Representatives from both the governing Zanu-PF and the opposition Movement for Democratic Change (MDC) are overseeing the collating process in Harare.
There is no indication when the result of March's election will be announced.
Earlier, MDC leader Morgan Tsvangirai insisted he had won an outright victory against President Robert Mugabe.
On Wednesday, government sources told reporters that Mr Tsvangirai had beaten the president, but had fallen short of the 50% needed to avoid a second round.
The opposition and human rights groups have accused the authorities of waging a campaign of violence to ensure Mr Mugabe wins any run-off vote.
Mr Mugabe was represented at the verification process at the Harare International Conference Centre by Rural Housing Minister Emmerson Mnangagwa, while Mr Tsvangirai was represented by his electoral agent, Chris Mbanga.
Zimbabwe Electoral Commission chief George Chiweshe said the rival parties would be able to compare results they had gathered at individual polling stations with the results compiled by the commission in order to agree on the final results.
Mr Mbanga was unsure how long the consultation would last, saying: "It may take one day, it may take two days, it may take one week, perhaps one month."
Earlier, the opposition criticised what it said appeared to be an official leak of results.
MDC spokesman Nelson Chamisa said reports that Mr Tsvangirai had won 47% of the presidential vote to Mr Mugabe's 43% appeared to be a rumour spread by the government to prepare people for a run-off.
Independent observers and Mr Mugabe's allies have said a run-off is likely to be needed as no candidate appears to have gained more than 50% of the vote.
"As far as I'm concerned, there is going to be a run-off," Deputy Information Minister Bright Matonga told the Associated Press. "We have got our own results."
Independent observers say a second round run-off is likely to be needed
But in an interview with French television, Mr Tsvangirai insisted he had won the 29 March vote outright, and that a second round was unnecessary.
Based on the results his supporters collected from individual polling stations, the MDC has "come up with a result which we feel is credible", he said.
"That result gives us a decisive victory so there's no need for a run-off," he told France 24 from Johannesburg in neighbouring South Africa.
"How can you have a run-off when Mugabe over the last month has been unleashing violence, death squads and violence against our structures?"
Despite such allegations, Mr Tsvangirai said that he would return to Zimbabwe when the official election result was announced.
Earlier, Zimbabwe's influential police chief accused the opposition of trying to rig elections.
Police Chief Augustine Chihuri said more than 100 cases of fraud by MDC agents had been found following last month's elections.
Mr Chihuri is one of the Zimbabwean security chiefs who reportedly persuaded Mr Mugabe not to step down immediately after the 29 March elections.
The MDC's Mr Chamisa says 20 people have now been killed in politically-motivated attacks in Zimbabwe since the polls.
Human Rights Watch (HRW) has accused the army of organising the attacks on MDC activists, by providing weapons and transport.