Guineans are voting in a controversial presidential election that is expected to see incumbent President Alpha Conde re-elected for a second term after a campaign plagued with accusations and violence.
Polling stations opened on Sunday with national borders closed for the day and traffic restricted to the vehicles of electoral observers, government officials and the security forces, according to a presidential decree.
Opponents of President Conde had called for the postponement over what they called the unreliability of the electoral lists and problems with distributing voter cards, which are required to cast a ballot.
The results of the first round are not expected until Tuesday at the earliest.
Conde's seven rivals vowed to challenge the results, raising the spectre of further unrest in the days to come, after deadly clashes between Conde and opposition supporters in the final days of campaigning.
An African Union observer mission and a 72-member European Union delegation are in Guinea to monitor the ballot, along with 19,000 police and members of the security services.
Conde is hoping to win the first round, avoiding a "run-off" election with his closest rival, but his opponents contend this feat would be impossible without vote-rigging.
Conde, whose campaign slogan promises to deliver a "knock-out blow" to his opponents, is hoping to trade on his five-year record of reforms in the impoverished but mineral-rich West African country.
Among his achievements, he cites an overhaul of the army and judiciary, the completion of a hydroelectric dam and reforms to make mining contracts more transparent.
"Ask the people of Guinea if what we have done in five years, the others did in 50. Ask that on the streets," he said in an interview.
Despite being rich in bauxite, the ore used to produce aluminium, the country is one of the world's poorest and was blindsided by a severe outbreak of Ebola, which began in the country's southern forests in December 2013, and then spread to neighbouring countries.
Half the population lives below the UN poverty line, and according to the World Bank, per capita income in 2014 was just $470 with many lacking access to electricity or running water.