Nazarbayev was so confident of defeating his four challengers he scheduled a rally at a sports complex in the capital, Astana, on Monday morning, just minutes after election officials plan to announce preliminary results.
A pre-election opinion poll by the U.S.-based Intermedia Survey Institute reported that Nazarbayev had 71 percent support, but it cautioned that the responses "may reflect some wariness by respondents to express their true attitudes."
Nazarbayev, who has ruled for 16 years, often shows an authoritarian streak, and opposition candidates claim their campaigns have been hindered by the theft of campaign materials, seizure of newspapers backing them and denial of attractive sites to hold rallies.
His two previous election victories were widely criticized as undemocratic. After voting Sunday in the capital Astana, Nazarbayev said "this year's elections are being held in unprecedented democratic conditions."
But the ITAR-Tass news agency later reported that Valdimir Rushailo, head of the monitoring mission of the Commonwealth of Independent States that includes most ex-Soviet countries, said observers had noted some violations at the station where Nazarbayev voted, including one person casting two ballots into a box.
Vladimir Petikhin, head of the Russian contingent of CIS observers, said his colleagues had not recorded any serious problems and "we can say the election took place practically without violations." As of 6 p.m., two hours before most of the country's polls closed, turnout was 68 percent, the Central Elections Commission said.
Bolat Abitov, campaign chief for main challenger Zharman Tuyakbai, said late Sunday that observers from the campaign saw many violations, including people being excluded from voter lists and some voters reportedly being ordered by officials or employers to cast ballots for Nazarbayev.
Kazakh officials have alleged that the opposition plans postelection disturbances similar to the protests in Georgia, Ukraine and Kyrgyzstan over the past two years that helped bring opposition figures to power.
Tuyakbai, who voted in Almaty, the country's commercial capital, said that if there is evidence of election fraud, he and his supporters "will use all legal means to resist."
Amid the crossfire of allegations of dirty tricks, the assessment of international election observers is likely to play a key role in how the opposition responds to the elections.
The observation mission of the Organization for Security and Cooperation in Europe, whose conclusions are widely regarded in the West as definitive, will issue a preliminary report Monday.
In pre-election assessments, the mission has cited opposition candidates' restricted access to media coverage as a potential hindrance to a fully democratic election. It also has expressed concern about the electronic voting system being offered as an option to paper ballots in about 15 percent of precincts.
Kazakhstan, four times the size of Texas and the world's ninth largest country by area, has vast oil and gas reserves that are a potential alternative to Middle East petroleum, and its stability matters greatly to the United States and Western Europe. The country also borders both Russia and China.
Under Nazarbayev, Kazakhstan has maneuvered between Washington, Moscow and Beijing. With Russia and China, it is a member of the Shanghai Cooperation Organization that has called for U.S. bases in the region to be closed. At the same time, a small Kazakh contingent is part of the U.S.-led coalition in Iraq.
Nazarbayev, who has led the nation of 15 million since 1989 when it was still part of the Soviet Union, is widely esteemed for his economic reforms, in contrast to Uzbekistan and Turkmenistan, also led by Soviet-era presidents.
Kazakhstan's economy has grown by some 75 percent over the past seven years, and per capita gross national income is about $2,250, about five times higher than neighboring Uzbekistan's.
Rival Tuyakbai promises to curb corruption, make democratic reforms, reduce poverty and distribute energy revenues more fairly.
Kazakhstan's comparative prosperity is Nazarbayev's strong suit, while dissatisfaction with him is rooted in Kazakhstan's inhibited political climate and allegations that he and his family have enriched themselves at the country's expense.