With opposition groups under what rights groups call a campaign of intimidation and abuse, there seems to be little doubt that the reforms will pass.
Nkurunziza is limiting presidential terms to two periods of seven years, but only from the next time he runs for re-election, in 2020.
"He's trying to do what a number of African presidents have done, which is to package what looks like a good democratic reform - i.e. 'I will bring in term limits and make sure they're respected, whilst at the same time, bringing in something that will allow him to extend his own power - i.e. creating longer terms so that he's able to stay in power for a longer period of time," said Nic Cheeseman, Africa specialist at Birmingham University in the UK, in an interview with RFI.
Assaults, verbal threats
In the referendum campaign, opposition groups have been allowed to rally for the first time since the country’s political crisis started in 2015. But according to Tchérina Jerolon, deputy head of the African office at human rights group FIDH, dissidents have also faced an intimidation campaign.
"A number of militants from the opposition have been arrested,” Jerolon told RFI. “There are a couple of people who were also beaten; there has been a couple of verbal threats pronounced by the ruling party, the CNDD-FDD. Pierre Nkurunziza himself, when he launched the referendum, was very explicit when he stated publicly that those who would oppose the referendum would be exposing themselves to serious consequences."
1200 killed since 2015
Burundi’s political crisis started in 2015 when Nkurunziza ran for, and won, a third term, in what many said was an unconstitutional vote.
Emmanuel Dupuy, Africa specialist and head of Paris-based think tank the IPSE, suggested in an interview with RFI that Nkurunziza launched this referendum to bolster his power after the turmoil that started in 2015.
"What is behind all of this is the fact that since the first civil society opposition towards the regime of Nkurunziza in April and May 2015, there was an ongoing uprising, leading to the deaths of more than 1200 people," said Dupuy.
The proposed reforms wouldn’t just lengthen Nkurunziza's time in office. They also allow ethnic quotas - seen as crucial to the peace after Burundi's 1993-2006 civil war - to be revised. They also take powers away from ministers and give them to Nkurunziza.
"He's removing some of the checks and balances that were put in place in the former system to prevent the abuse of power,” said Cheeseman.
“Some of that will be significant but I think that we also need to keep in mind that, although those rules were formally on the books, they weren't really being respected previously – so in some ways what this is, is formalising what was already happening,” he told RFI.
Cheeseman continued: “One of the things that's really worrying though, is the removal of ethnic quotas. These were introduced after a long period of political instability and civil war as a way of giving all communities a stake in the political system.
The idea was: by using quotas, everyone would feel included, everyone would get a share of resources and a share of jobs, and that would prevent a return to conflict. By removing those, he signalling a return to 'winner takes all' politics - and that could have very serious consequences for political stability in Burundi going forward."