Japarov, a 52-year-old populist, has brushed aside political opponents since coming to power on the back of an October political crisis in which he was first released from jail by supporters, beginning a dizzying rise to the leadership.
He confirmed his dominance by posting a landslide victory in a presidential election in January that also saw voters indicate a preference for presidential over parliamentary rule in a parallel vote, boosting his drive to overhaul the basic law.
Two of his opponents on the ballot and a former prime minister were arrested in the weeks after the vote as Japarov and his allies further cemented their control.
The new leader’s proposed constitutional amendments promise a presidency in line with impoverished Kyrgyzstan’s Central Asian neighbours, ending a decade-long experiment with a mixed system.
Local critics have dubbed the draft document a “khanstitution” for its expansion of presidential powers of appointment at the expense of parliament, which will be downsized from 120 to 90 lawmakers if the changes pass.
The Organisation for Security and Cooperation in Europe and the Council of Europe’s Venice Commission criticised the lack of “meaningful and inclusive public consultations and debate in parliament” before the basic law was put to the people in a joint opinion published in March.
The two bodies also raised fears over the “overly prominent role and prerogatives of the President”.
President Vladimir Putin of Russia, a key ally, expressed support for the constitutional drive in February when Japarov went to Moscow in his first foreign visit, saying that he hoped it would bring stability to the country of 6.5 million.
Japarov’s predecessor, Sooronbay Jeenbekov, became the third Kyrgyz president to resign during a political crisis since the country’s independence from the Soviet Union in 1991 last October.
If voters back the draft constitution, presidents including Japarov will be able to run in consecutive elections once more, reversing the single-term limit imposed on leaders during an overhaul of the basic law in 2010.
That change was championed as a safeguard against entrenchment after two revolutions in the space of five years unseated authoritarian leaders and their powerful families.
Voting in the referendum began at 0200 GMT and will conclude at 1400 GMT with results expected shortly after polls close and a 30 percent turnout required to validate the election.