Polling stations in the Democratic Republic of Congo have begun posting interim results, after the first multi-party election in 40 years.
An official result is not expected for some weeks
Full results of Sunday's polls are not expected for weeks.
The elections were aimed at ending a long civil war, with 32 candidates, including incumbent Joseph Kabila, contesting the presidency.
Over 9,000 candidates stood for parliament. Some 25m voters were protected by 17,000 UN peacekeepers.
It is still far from clear whether a second round will be required, or whether a candidate will gain the 50% of the votes needed to win outright, the BBC News website's Joseph Winter reports from Kinshasa.
The RCD party, led by former rebel and Vice-President Azarias Ruberwa, told our correspondent there had been "widespread fraud".
RCD Secretary General Kabasu Babu Katulondi said RCD representatives had been chased out of polling stations when counting started, while ruling PPRD officials had been caught trying to vote more than once.
"The delay is one of Kabila's tricks to manipulate the figures," he said.
Results from several polling stations seemed to back up pre-election predictions that former rebel leader and Vice-President Jean-Pierre Bemba would win most votes in Kinshasa.
However President Kabila was expected to win more votes in eastern DR Congo, where he is credited with ending the war.
Thomas Luaka, a spokesman for Mr Bemba's MLC party said that while he "deplored some incidents, overall, the elections went well".
Earlier, Mr Bemba's supporters had demonstrated on the streets of the capital, Kinshasa, saying they were cheated.
Independent Electoral Commission official Carole Kabanga Kaoy said she could not comment on the allegations of fraud until she had received official reports, at which point each party would be free to provide evidence of irregularities.
Congolese describe their election hopes and fears
Mr Kabila, who came to power unelected in 2001, has told the BBC he will accept the result of Sunday's presidential elections, even if he loses.
"It would have been the verdict of the people and of course we will definitely accept the verdict of the people," he said.
Opposition leader Etienne Tshisekedi and his UDPS party boycotted the vote.
There were reports of violence on election day in Mr Tshisekedi's stronghold, the south-eastern Kasai region.
But a United Nations official said he was "relieved" and "delighted" with how the voting had gone.
"All indications that we have, not just from Kinshasa, but across the country is that the population has responded fairly substantively," UN envoy Ross Mountain said.
"The number of incidents have been absolutely minimal. The security hasn't been a problem and it has been an extraordinary day for Congo."
BBC world affairs correspondent Mark Doyle says the real test of the elections will be the acceptance of the results by all of the former warring parties.
The presidential candidates include the four vice-presidents who took office in 2003 in terms of a transitional power-sharing deal.
Three of the four vice-presidents are the leaders of former armed factions.
Some opposition candidates accuse Mr Kabila of being backed by the international community, and are already unofficially complaining about what they say are irregularities in the voting, our corresponent says.