Opposition allegations of fraud, as well as a row between Western election monitors and Kazakh officials, cast a shadow over the vote in the ex-Soviet republic on Sunday, forecast to become one the world's top 10 oil producers within a decade.
Voters appeared enthusiastic as they queued up in the capital, Astana, in darkness and freezing temperatures for the opening of polling stations at 7am (0200GMT).
"Of course I'll vote for the current president," pensioner Margarita Alexandrova, 65, said at polling station 153. "The opposition does not inspire confidence."
"I'm voting for Nazarbayev," 50-year-old teacher Ainur Akhmedova said after casting her ballot at another polling station. "We know him better."
Kazakhstan, roughly the size of western Europe or India and once part of Genghis Khan's empire, has never held a poll judged free and fair by Western observers.
"I'm voting for Nazarbayev, we know him better"
Ainur Akhmedova, a teacher
Nazarbayev, 65, faced four challengers, led by former prosecutor-general and ex-parliament speaker Zharmakhan Tuyakbai, and former labour minister Alikhan Baimenov.
Also running were Mels Yeleusizov of the environmentalist Tabigat movement and Yerasyl Abilkasymov of the People's Communist Party.
The president is believed to enjoy solid support thanks to growing prosperity in the country, a former Soviet backwater that has recently seen billions of dollars of foreign investment go into its Caspian Sea oilfields.
Government polls and independent analysts predict the president, who first came to power as communist leader in Soviet Kazakhstan in 1989, will get at least 50% and avoid a second round of voting.
However, the opposition says that media bias and pressure from the authorities skewed the campaign. Tuyakbai, who is seen as the main challenger, followed by Baimenov, has warned of a slide towards dictatorship.
The communist candidate, Abilkasymov, said that the names of his family were not on voter-lists in his home precinct in Astana.
"There's disorder and chaos," he told reporters. "If they didn't put even relatives of a presidential candidate, then what about the others?"
The Organisation for Security and Cooperation in Europe (OSCE) sparked fury on Saturday in declaring that the Kazakh government had not fulfilled most of the 24 recommendations made in an OSCE report on preparations for the election.
"No, they have not. They have implemented a few of the recommendations," spokeswoman Urdur Gunnarsdottir told AFP, adding that a "good election" was still possible.
Opposition figures such as Tuyakbai
have alleged voting irregularities
A top official from the Kazakh Central Elections Commission, Marat Sarsembayev, said the OSCE statement had "caused bewilderment."
"The observers from the OSCE non-objectively and unprofessionally broadened their demands," he said. "All 24 recommendations which were presented in the report ... have been fulfilled."
Polls were to close at 8pm (1500 GMT) nationwide.
About 8.6 million voters were eligible to vote. No minimum turnout is required.
About 1600 observers are monitoring the election, including 465 from the OSCE.