Burundi is voting in a referendum proposing constitutional changes that could extend the president's rule until 2034.

Five million people are registered to vote in the referendum amid fears of violence because of President Pierre Nkurunziza's efforts to prolong his stay in power despite widespread opposition.

Burundi descended into violence in 2015 when Nkurunziza sought a disputed third term.

In Bujumbura, the capital, there are long lines of voters and the security forces have been deployed across the city.

If the results of the referendum go his way, Nkurunziza could get an additional 14 years in power when his current term expires in 2020.

Rights groups cited there have been abuses targeting opponents of the proposed constitutional changes.

It is not clear when final results will be announced.