Gunfire rang out across Guinea's capital Conakry on Friday and security forces dispersed protestors after results showed President Alpha Conde winning re-election in a poll that the opposition says was unconstitutional.

Conde won around twice as many votes as his nearest rival, opposition candidate Cellou Dalein Diallo, with 37 of 38 districts counted, preliminary results from the election commission showed on Thursday night.

The president's decision to run for a third term has sparked repeated protests over the past year, resulting in dozens of deaths, including at least 17 in skirmishes since Sunday's vote.

Conde says a constitutional referendum in March reset his two-term limit, but his opponents say he is breaking the law by holding onto power. Diallo's camp said it has found evidence of fraud and will contest the result in the constitutional court.

Gunfire was heard Friday in the Sonfonia neighbourhood of Conakry, where Diallo supporters clashed with security forces, witnesses said.

"There were warning shots. The police intervened to clear the barricades and disperse the demonstrators," Oumar Camara, a local resident, told Reuters.

Friday's violence follows a series of clashes on Thursday in which four were killed, security minister Damantang Albert Camara told Reuters.

Internet and phone access were severely disrupted on Friday morning, digital rights groups and witnesses said. Authorities in Guinea, as in much of sub-Saharan Africa, have in the past cut internet access to sever communications during times of unrest.

The government was not available to comment on internet access on Friday, but network data for Internet monitoring group NetBlocks showed that the internet was disrupted from 0730 GMT on Friday morning, including on leading cellular operator Orange.

"The incident has nation-scale impact ... and is likely to significantly limit the domestic and international flow of information," NetBlocks said in a statement.