CONAKRY Guineans used to decades of harsh authoritarian rule elect a president Sunday in the West African state's first free elections since independence from France in 1958.
The run-off poll, if it passes peacefully, could mark a turning point for the minerals-rich country and bolster efforts to develop democracy in Africa's "coup belt."
But experts say there is a high risk of ethnically-driven violence if the results are challenged.
The run-up to Sunday's vote has been turbulent, with deadly clashes between rival political camps and rows over electoral preparations leading to delays to the decisive second round since the first vote was held in June.
International observers were hopeful that electoral officials had laid the groundwork for a free and fair run-off to reduce the chances the results will be rejected by the loser over allegations of fraud.
"I am confident that all that can be done has been done. The (electoral commission) has done its utmost - of course nothing is perfect," Said Djinnit, the head of the United Nations Office for West Africa, told Reuters by telephone.
The vote will end nearly two years of junta rule since a December 2008 coup, and will come close on the heels of Ivory Coast's October 31 first round of presidential elections, which passed peacefully despite some worries of turmoil.
Guinea's run-off pits former Prime Minister Cellou Dallein Diallo against veteran opposition leader Alpha Conde -- each representing one of Guinea's two most populous ethnic groups, the Peul and Malinke, respectively.
The stakes are high for the world's top supplier of aluminum ore bauxite, whose resource riches have attracted billions of dollars of planned investment from companies like Vale and Rio Tinto but where instability has hampered development.
Diallo took 43.69 percent in June's first round -- making him the favorite -- while Conde, who later complained of fraud undermining his score, took just 18.25 percent.
Tensions run deep between Peul supporters of Diallo and Malinke supporters of Conde after recent clashes, with neither group likely to easily accept their candidate's loss.
"If Conde loses, the election will have been fraudulent," said Amadou Camara, a Malinke taxi driver and Conde supporter.
The Peul, meanwhile, have long believed other ethnic groups have ganged up to keep them out of power since independence.
Analysts have warned that ethnic tensions pose some risk to neighbors Liberia, Sierra Leone, and Ivory Coast -- all of which are still recovering from recent civil wars and which share Peul and Malinke populations.
(additional reporting by Mark John; editing by Ralph Boulton)