If Thursday’s referendum vote is passed, the constitution will be amended to extend the president’s term from five to seven years. The changes will also allow President Nkurunziza to stand for two more terms after his current one comes to an end in 2020.
Polls opened at 0700 GMT and will close at 1200GMT.
The referendum needs to be approved by more than 50 percent of the voters for the proposed changes to be made.
Some 4.8 million people, a little under half the population, have signed up to vote, according to the Independent National Electoral Commission (CENI), which is running the referendum.
“I cast my vote today so that we can get the leaders we deserve. This referendum gives me the choice to choose leaders that can change my life,” Citegetse Janvier, a businessman, told Al Jazeera shortly after casting his ballot.
“I’m very happy I came out to vote. I cast my vote because I want peace to return to our country,” Hatungimana Modeste, a farmer, told Al Jazeera.
Nkurunziza, a former rebel leader and born-again Christian, came to power in 2005 after the warring sides in the country’s civil war signed a peace deal in the Tanzanian city of Arusha.
A provision in the peace agreement said no leader could serve more than two five-year terms. But Nkurunziza, arguing that he had only been directly elected by the people once, run for a third term in 2015 leading to deadly violence that led to the death of more than 1,200 people and displacing 400,000 others.
The ballot is taking place in tightly-controlled conditions, and a presidential decree ruled earlier this month that anyone advising voters to boycott the vote risks up to three years in jail. DM