The African nation is voting on a new parliament to replace the transitional parliament that has been seated since military rule ended in 2010.
Anger and suspicion led to scattered violence around Guinea this week that left a police officer dead and about 70 people injured, the Voice of America said.
The opposition said it suspected President Alpha Conde's party would try to fix the election in its favor.
"Alpha Conde invents a permanent conspiracy so that he can blame our party. These are old demons coming back, but they do not weaken us," opposition leader Cellou Dalein Diallo said Friday.
A spokesman for Conde's party, on the other hand, said, "We are already savoring our victory."
The BBC said Saturday's election was held after two years of delay since the military stepped aside. The voting was postponed repeatedly amid ethnic violence and opposition allegations the voting was being rigged.
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