Guinea's President Alpha Conde has won a landslide re-election victory, preliminary results showed on Thursday, giving him a third term in office after a bitterly fought election that has sparked deadly street violence.

With 37 of 38 electoral districts counted, Conde, 82, received 2.4-million votes, versus 1.26-million for his nearest rival, opposition candidate Cellou Dalein Diallo.

"We are satisfied with the first results which give us hope and confidence for a certain victory," Conde spokesperson Tibou Kamara told Reuters.

Conde's decision to run for a third term has sparked repeated protests over the past year, resulting in dozens of deaths, including at least 13 in skirmishes since Sunday's vote.

It has also raised concerns that he and other rulers in the region are undermining the progress that West Africa has made towards multi-party democracy since the 1990s. Ivory Coast has seen similar clashes this week as President Alassane Ouattara seeks a third mandate in an election later this month.

Like Ouattara, Conde says a recent constitutional referendum reset his two-term limit. But his opponents say he is breaking the law by holding onto power, and that they will contest the results.

The rainy streets of the capital Conakry were calm after the results on Thursday night, according to witnesses across the city, though the political tension remained high.

"The results ... are not in line with what happened on polling day. We have the evidence of the fraud and we will challenge all of this in the Constitutional Court," said Diallo spokesperson Aliou Condé, without providing any evidence.

Diallo has claimed victory based on his own campaign's tallies.

A spokesman for CENI, the election commission, defended the election on Thursday as the "most transparent and the cleanest that has ever been organized in Guinea".

He said official numbers showing more votes than registered voters in one district was a "typing error".