Kazakh President Nursultan Nazarbayev is heading for re-election by a wide margin, exit polls suggest.
Nursultan Nazarbayev has been in power for 16 years
Various polls showed the incumbent had won between 77% and 87% of the vote.
However, the opposition complained of "multiple violations" in the election. Previous votes in Kazakhstan have been adjudged neither free nor fair.
Mr Nazarbayev has headed the oil-rich Central Asian state since 1989 - two years before independence. A win would mean a further seven years in power.
According to the exit polls, Mr Nazarbayev's nearest challenger was Zharmakhan Tuyakbai, with between 9% and 13% of the vote.
Preliminary official results are expected on Monday.
Mr Nazarbayev said the elections were held in "unprecedented democratic conditions".
Speaking after casting his vote in Almaty, he said all five candidates had equal conditions and the same media access.
However analysts from the Assessment Risks Group NGO in Almaty say his rivals had very limited exposure during campaigning from a media which is largely under government control.
Opposition candidates have complained that they had no chance of putting across their message to voters.
The election is being seen as an important test of whether this vast country is moving towards greater political openness, says the BBC's Ian MacWilliam in the capital, Astana.
About 450 monitors from the Organization for Security and Co-operation in Europe and the European Parliament have been observing the poll and will hold a news conference about their findings on Monday.
Parliamentary elections last year were widely seen as rigged.
Mr Tuyakbai, a former prosecutor general and parliamentary speaker, said before Sunday's election he expected it to be "fraudulent".
However, analysts say Mr Nazarbayev is genuinely popular among voters.
Voters are in a more upbeat mood than they have been in many years, our correspondent says, as after more than a decade of post-Soviet drabness and depression, Kazakhstan is suddenly on the edge of an oil-fuelled boom.