Ghana's opposition New Patriotic Party has accused the governing party of fixing the result of Friday's election.
The NPP said in a statement that the National Democratic Congress conspired with Electoral Commission staff to boost its tally across the country.
There has been no response from the NDC or the commission.
Local media reported partial results showing NDC candidate President John Mahama had a narrow lead over NPP rival Nana Akufo-Addo.
Joy FM said Mr Mahama looked likely to gain more than 50% of the vote, which would give him overall victory without needing a run-off vote.
Ghana, one of the world's fastest growing economies, is regarded as one of Africa's most stable democracies.
Mr Akufo-Addo lost the 2008 presidential poll by one percentage point, but accepted the result.
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