The country's Central Election Commission said the turnout was 89.69 per cent by 1200 GMT with polling set to continue until 1400 GMT.
The marginalised opposition in the energy-rich former Soviet state has not put forward any candidates for the election and Nazarbayev is standing against two candidates widely seen as pro-government figures.
Nazarbayev has ruled the Central Asian country since before the breakup of the USSR in 1991. If he wins a new five-year term, he will be on course to reach three decades as leader.
"I am sure Kazakhstan's people will vote primarily for the stable development of our state and the improvement of people's lives, as well as the stability of the state and in support of the policies the country has implemented under my leadership," Nazarbayev told journalists.
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"I am confident of this."
Many citizens standing in long, snaking queues at polling stations in the capital Astana and second city Almaty cited a "civic duty" to vote.
Gulmira Bardygulova, a student in the country's largest city, Almaty, said she had voted for Nazarbayev to save the country from political turmoil.
Some, though, complained of having been pressured to turn out to vote by their employers.