Voters in Guinea are voting in a controversial election that sees President Alpha Condé, 82, running for a third term.
The already severely divided West African country was gripped by tensions on Friday after gunmen killed a senior army officer in a military camp.
Mr. Condé ignored criticism to push for a constitutional change that allowed him to extend his term.
His main challenger is Cellou Dalein Diallo, whom he has beaten twice.
Ethnic clashes during the campaign have raised fears of nationwide violence if the results are contested.
The government has closed borders with some neighboring countries, citing security reasons.
Some 5.4 million voters are eligible to vote. The results are not expected for several days.
Candidates need more than 50% of the vote for an outright victory, or there will be a second round on November 24.
The fears of military divisions
Guinea has been plagued by an authoritarian and military regime since its independence. There were fears that the military could get involved in politics again.
On Friday, the defense minister released a statement saying a group of soldiers entered a military camp in Kindia, a town 130 km east of the capital Conakry, and killed its commander, Col Mamady Condé.
There were reports of an army mutiny, but authorities later said they were in command and a search was underway to locate the soldiers.
Five things about Guinea:
Independence leader Sékou Touré told France in 1958: “Guinea prefers poverty in freedom to wealth in slavery”
‘Black power’ civil rights leader Stokely Carmichael left the United States for Guinea in 1968 with his then-wife singer Miriam Makeba becoming a lifelong supporter of Pan-Africanism.
It has the largest reserves of bauxite in the world – the main source of aluminum
Its Mount Nimba Strict Nature Reserve, a Unesco World Heritage Site, is known for its viviparous toad and chimpanzees that use stones as tools
Singer Mory Kanté, famous for the 80s hit Yéké Yéké, comes from a family of well-known Guinean griots, or singers of praise
Who is Alpha Condé?
Mr. Condé was a veteran of the opposition who finally won the elections in 2010, marking the first truly democratic transfer to Guinea since independence.
He served a prison sentence for challenging General Lansana Conté, who reigned from 1984 until his death in 2008.
He campaigned on his economic record and the prospects that Simandou, one of the world’s largest untapped iron ore deposits, could finally be mined – creating thousands of jobs.
But critics say not all economic growth has spilled over to the bulk of the population.
A new constitution was approved in a referendum in March. Mr Condé argues that this means he is allowed to seek re-election, even though he had already served the maximum of two terms allowed by the previous constitution.
The opposition disputes this and street protests have left dozens of people dead over the past year.
Who is its main challenger?
Cellou Dalein Diallo, 68, former Prime Minister, is the only formidable opponent. He lost to Mr Condé in 2010 and 2015, although he claims both elections were marred by widespread fraud.
He is a member of the Peul, or Fulani, the largest ethnic group in Guinea. The country has never had a Fulani president and many ethnic Fulani claim that their community has been discriminated against, dating back to the days of President Sékou Touré, when thousands fled the country.
Mr. Condé is widely supported by members of his Malinké community, as well as by the country’s third major ethnic group, the Soussous.
He and other opposition figures from the National Front for the Defense of the Constitution (FNDC) had vowed to boycott an election which they believed could never be fair.
But in early September, Mr. Diallo broke with the FNDC, announcing he would run after all.