Guinea's authorities imposed an overnight curfew on the second city of Nzerekore after clashes left at least one person dead, local media report.
Fighting broke out on Saturday after a campaign visit from President Alpha Conde who is running for re-election.
Backers of the president clashed with supporters of his rival Cellou Dalein Diallo in this hotly contested city.
Opposition parties have called for Sunday's election to be postponed over alleged irregularities in the process.
Nzerekore is the stronghold of former military junta leader Moussa Dadis Camara, who recently attempted to return to Guinea from exile to run for president.
His party has now entered an alliance with Mr Diallo.
In addition to the one fatality, more than 80 people were wounded by "gunshots or stones" in the fighting, according to a medical charity quoted by the AFP news agency.
More than a dozen people were injured in the northern town of Koundara as rival groups clashed at the end of September.
President Conde is facing seven challengers in the second election since the death of the long-serving leader Lansana Conte.
Mr Conde won the 2010 election after a second-round run-off against Mr Diallo.