Despite the threat of coronavirus and an opposition boycott, a constitutional referendum was held in Guinea on Sunday that opponents of President Alpha Conde fear could allow him to govern for 12 more years.

Opposition supporters heeding a call to disrupt the referendum and simultaneous legislative election attacked several polling stations in the capital Conakry, delaying the start of voting in some districts.

Security forces were quick to contain the pockets of unrest and there was no immediate report of significant casualties.

The opposition boycott all but ensures the new basic law will be approved when results are announced in the coming days, despite the risk it could trigger wider unrest that would, along with coronavirus, threaten Guinea's mining economy.

With the first two cases of the Covid-19 disease recorded in the country, some polling stations required voters to wash their hands before casting their ballot and radio stations reminded citizens to keep their distance from one another.

"Even if people are aware (of the coronavirus risk), that won't stop those who want to come out and vote. I'm trying not to stand too close to others because you never know," said 26-year-old student Ndeye Toure after voting.

At some polling stations, a large turn-out meant crowds were squeezed in line to vote, according to a Reuters witness. Few people wore masks.

Conde, 81, has refused to rule out using a new constitution as a reset button on his mandate, which expires in December, citing other African countries as examples of where leaders have extended their rule.

The referendum, originally scheduled for March 1, was postponed because international observers raised concerns about the electoral register.

The confirmation of coronavirus raised speculation last week the polls could be further delayed, but the authorities have stuck to the schedule despite banning other large gatherings to prevent the spread of the disease.

The new constitution would impose a limit of two six-year terms, up from the current two five-year terms. It does not specify whether terms served under the previous constitution would count, but Conde has suggested they would not.

At least 30 people have died since October in protests against the proposed changes. The vote could be a bellwether for a presidential election before year's end in the country, the largest African producer of the main aluminium ore, bauxite.