The opposition has already said it expects the election to be riddled by fraud.
Opposition challenger Zharmakhan Tuyakbai said after he voted in the biggest city Almaty that there are first alarming signals from the provinces where there have been a number of violations.
He said his campaign has evidence of duplicate voter lists that could allow multiple voting.
In the country's new capital Astana, Nazarbaev said after casting his ballot that "this year's election is being held in unprecedented democratic conditions." He also said he expects Kazakhs to vote for stability.
"I am sure that the Kazakh people will choose political stability, friendship, and unity for our multiethnic people -- that they will choose the progress of the state in this direction and that soon the Kazakh state with its people will become one of the top 50 most-industrialized countries of the world," Nazarbaev said. "We will maintain the stability of our country. The economy will be growing. And with economic growth, the living conditions of our people will improve."
Early results from a controversial Belarus-designed electronic voting system that is used alongside paper ballots are expected tomorrow.
(with material from agency reports)