People are eager for the results, which are being released slowly
Zimbabwe is standing on a "precipice" as official results from Saturday's general election slowly emerge, the opposition has said.
Senior Movement for Democratic Change official Tendai Biti says party leader Morgan Tsvangirai has won 60% of the vote, against 30% for Robert Mugabe.
Official results show Zanu-PF has 31 parliamentary seats, while the opposition has 35 altogether, so far.
Two senior Zanu-PF ministers are among those to have lost their seats.
Justice Minister Patrick Chinamasa lost his seat, east of Harare. Public Affairs Minister Chen Chimutengwende has also lost his seat in Mazowe, seen as a stronghold for President Mugabe's Zanu-PF party.
The BBC's Ian Pannell, reporting from Zimbabwe despite the BBC being banned from operating there, says the situation is calm, but there is an air of expectation and suspense.
Most people he has spoken to say they believe Mr Mugabe has been beaten and he must now leave office, our correspondent reports. But they also warn that there have been false dawns before, he adds.
Local results have been posted outside most polling stations since Sunday morning.
Five seats have gone to a breakaway faction of the MDC, according to official results.
MDC spokesman Nelson Chamisa told the BBC his party had won 99 of the 210 parliamentary seats, against 96 for Zanu-PF and 15 for other opposition parties, based on his party's final figures.
ELECTION RESULTS SO FAR
Breakaway MDC faction: 5
Yet to declare: 144
None so far
Winner needs more than 50% to avoid run-off
Results according to MDC:
Morgan Tsvangirai, MDC: 60%
Robert Mugabe, Zanu-PF: 30%
MDC 99 parliamentary seats
Other opposition 15
Mr Biti said the electoral commission was planning to announce that Mr Mugabe had won 52% of the vote - just enough to avoid a run-off. The MDC would not accept these results, he said.
Deputy Information Minister Bright Matonga denied the polls would be rigged and said the president would accept defeat.
He said people should be patient in waiting for the results.
"The verification process is ongoing. They are announcing the results," he told the BBC. "I know everyone is very anxious, they are on edge. They don't know if they are going to make it or not."
Mr Matonga also denied rumours that Mr Mugabe had gone to Malaysia or was planning to impose a state of emergency.
Riot police have been patrolling the capital, Harare, and other urban areas and residents have been told to stay indoors.
A senior Zanu-PF source has told a BBC contributor that security officials met on Sunday to decide who should tell Mr Mugabe he had lost, with some refusing to take the job.
In the southern town of Masvingo, MDC supporters have reportedly stopped celebrating since reports came in that Zanu-PF had won in areas initially believed to have gone to the opposition.
Presidential, House of Assembly, Senate and local elections were all held on Saturday, and election officials say that this is why results have been slow to come.
Some Zanu-PF supporters have been celebrating the results
"It's an absolute necessity that all results be meticulously analysed at this stage," George Chiweshe, the chairman of the Zimbabwe Electoral Commission, said earlier.
But Noel Kututwa, the head of the Zimbabwe Election Support Network, said: "The delay in announcing these results is fuelling speculation that there could be something going on."
Poll monitors from the Southern African Development Community (SADC) said the elections had been "peaceful and credible".
But two SADC members from South Africa refused to sign a generally positive preliminary report of the mission, with one of them calling the polls "deeply flawed".
Western observers were banned from the election but a European Union spokesman urged the ZEC to announce the results to "avoid unnecessary speculation".
A White House spokesman said the US was concerned about the delay and urged "the election commission to count every vote honestly and to release results quickly".
UK Prime Ministrer Gordon Brown said the eyes of the world were on Zimbabwe.
"Two things are very important: first of all, that the election results appear and appear quickly so that people know what is happening on the ground and nothing is delayed," he said.
"And secondly, that the elections are seen to be fair."
A new monitoring group, the Independent Results Centre, backs up the MDC's claims of victory, saying Mr Tsvangirai has won 52% of the vote in the presidential race, against 41% for Mr Mugabe and 7% for independent candidate Simba Makoni.
Mr Chamisa said that MDC polling agents had been chased away from some polling stations on election day, which later recorded huge Zanu-PF victories.
He pointed to the case of Uzumba-Maramba-Pfungwe constituency east of Harare, where the Zanu-PF candidate received 15,000 votes against 2,000 for the MDC.
HAVE YOUR SAY
This delay is getting people agitated, we are all wondering what is going on
Of the seats declared so far, both parties have done well in their traditional strongholds - Zanu-PF in rural areas and the MDC in towns and cities.
But Zanu-PF has won one seat in Harare, while the MDC has gained six rural seats, including that of Mr Chinamasa.
The BBC's Grant Ferrett in Johannesburg says Mr Chinamasa has been an energetic and loyal supporter of Mr Mugabe, pushing through his land redistribution programme in defiance of court rulings.
Government spokesman George Charamba warned the MDC against claiming victory before official results are announced.
"It is called a coup d'etat and we all know how coups are handled."
After voting in Harare, Mr Mugabe, 84, who has been in power since 1980, said: "We don't rig elections. I cannot sleep with my conscience if I have rigged."
The MDC says it is fighting to save Zimbabwe's economy.
The country has the world's highest inflation rate, at more than 100,000%, and just one adult in five is believed to have a regular job.