The reform, promoted by President Kassym-Jomart Tokayev on March 16, intends to introduce a new governance model to the country and initiate a new era also known as 'New Kazakhstan' or the second republic.
Kazakhstan votes on a constitutional reform package promoted by President Kassym-Jomart Tokayev as a step toward liberalising the Central Asian republic, though it would still leave key powers in his hands.
Around 11.7 million people are eligible to vote in Sunday's referendum.
The reform is likely to provide Tokayev, 69, the political capital he needs to run for a second term in oil-rich Kazakhstan, this time without the backing of his predecessor Nursultan Nazarbayev.
Although in power since 2019 following Nazarbayev's abrupt resignation after three decades in power, Tokayev has only fully emerged as an independent figure this year after putting down an attempted coup in January and removing Nazarbayev and his relatives from key positions in the government.
Aside from moves to decentralise decision-making and allow greater representation of various groups in parliament, the reform will also strip Nazarbayev of his "national leader" status which granted him lifetime privileges.
The president, however, would retain powers to appoint judges and regional governors and dissolve parliament.
Tokayev has described the proposed changes as a move from a "super-presidential" system to a presidential republic with a strong parliament. Although critics say the reform is cosmetic, it does signal a reversal from a decades-long trend towards strengthening presidential powers.
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Foundation for 'Second Republic'
"We are... laying the foundation for the Second Republic," Tokayev said, addressing the nation on the eve of the vote.
He voiced confidence on Sunday that his initiative would pass: "There is a lot of work ahead, we will need to implement the constitutional provisions for which we are voting."
Almost 44 percent of voters cast their ballots by midday, the Central Election Commission said. Some, however, complained that the proposed changes to more than 30 articles of the constitution were too complicated.
"Have you read those amendments? It is a puzzle," said Natalia, 64, who declined to give her last name and chose not to vote.
Analysts said the move was in part a response to January's unrest which started as a protest against a fuel price hike and evolved into a broad display of public discontent with a system that concentrates power and wealth in the hands of a few.
Tokayev has also called for higher taxes on the lucrative extractive industries and high-income individuals, saying social justice would be the cornerstone of a new social contract.