Guineans cast ballots for a president on Sunday, with the 82-year-old incumbent Alpha Condé facing his longtime rival Cellou Dalein Diallo for a third time.
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Some 5.4 million people were registered to vote, and initial results are expected to be announced in several days.
Ten other candidates besides Condé and Diallo were contesting the poll. A second round run-off vote is scheduled for November 24, if needed.
Polls closed at 6pm local time after a mostly calm day of voting, but there are already fears of post-election discord.
"Alpha Condé cannot abandon his desire to grant himself a presidency for life," Diallo told reporters on Sunday, warning his rival not take power using "cunning and violence".
Security Minister Albert Damantang Camara told AFP there had been "no major incidents" on Sunday, but that he was concerned about suggestions that Diallo would not accept the result.
He urged him to "return to his senses".
'We want peace, not a fight'
Mohamed Fode Camara, a social affairs ministry employee, said he "feared the day when results are announced".
"God will save us, inshallah," he said, adding that Guineans "want peace, not a fight".
Much of the tension in Guinea relates to a new constitution Condé pushed through in March, in defiance of mass protests, arguing that it would modernise the country.
The move controversially allowed him to bypass a two-term limit for presidential terms.
After decades as an opposition activist, Condé became Guinea's first democratically-elected president in 2010 and won again in 2015 but rights groups now accuse him of veering towards authoritarianism.
Wearing an off-white suit, the president cast his ballot in a school for the deaf and said he wanted a "free, democratic and transparent" election, with no violence.
Diallo, 68, was formerly a prime minister under authoritarian leader Lansana Conté.
He cast his vote, dressed in a white robe, in the Conakry suburb of Dixinn, an opposition stronghold. Earlier, he had urged his supporters to "show restraint".
String of West Africa votes
Condé and Diallo have faced off twice before in tense polls in 2010 and 2015, but this year's were especially fraught.
The old rivals traded bitter insults on the campaign trail. Diallo frequently raised the issue of Condé's age and encouraged him to "retire with dignity".