ACCRA - Ghana's incumbent President John Dramani Mahama on late Sunday was declared winner of the Dec 7 presidential election for a four-year term starting next January.

National Electoral Commission (EC) Chairman Kwadwo Afari-Gyan told a packed press conference that Mahama took 50.7 percent of the vote, narrowly avoiding a run-off, while his closest rival Nana Akufo-Addo of New Patriotic Party (NPP) won 47.7 percent.

John Dramani Mahama, Ghana's interim president and the National Democratic Congress (NDC) presidential candidate, smiles at his home in Accra, on Dec 9, 2012. [Photo/Agencies]

The election actually was a two-horse race between Mahama of the ruling National Democratic Congress (NDC) and Akufo-Addo of the main opposition NPP as the six other candidates fared very poorly, obtaining less than 2 percent of the total votes cast.

Celebrating Mahama's victory, NDC supporters thronged the thoroughfares of the capital city, singing and dancing while beating drums, blaring music, chanting slogans and honking horns.

In a victory speech at his residence in Accra, the 54-year-old Mahama urged all candidates to respect the verdict of the Ghanaian people, and appealed to his supporters to exercise restraint in celebrations so as not to affect peace and stability of the country.

He expressed his appreciation of the people's confidence in him, promising to do his best for the Ghanaians.

Mahama, who only took over presidency last July following the sudden death of his predecessor John Atta Mills, also commended the country's electoral body for doing a good job in spite of some challenges in the process.

The NPP, however, rejected the official election results, claiming the polls had been manipulated and rigged.

In a statement issued on Sunday, the party said they had serious reservations about the validity of the results declared by the Electoral Commission.

It also said it had evidence that the election did not reflect the mandate of the required majority of the Ghanaian electorate. But it called on its supporters to remain calm.

There was heavy security presence throughout the country, particularly in the capital to brace for any disturbances or violent clashes between members of rival political parties.

Despite a few glitches such as the failure of some newly-introduced electronic fingerprint readers to identify voters, the election was generally considered by both local and international observers as calm, fair, transparent and peaceful.

"Ghana has come a long way since 1992 in her commendable efforts to ensure transparent and credible electoral management processes, and strengthen democratic culture. All stakeholders therefore have a responsibility to preserve these achievements," the Economic Community of West African States (ECOWAS), which also dispatched observers to monitor the election, said in a statement.

Since its return to civilian rule in 1992, Ghana has held six successive successful general elections. The NDC has won four of them while the NPP has won two.

Ghana is a top exporter of cocoa and gold, with an economic growth of 14 percent in 2011. An 8-percent growth is expected this year and the following.

Ghana also started oil production two years ago. How to spend Ghana's newfound oil money has been a key issue in the election.