Malaysians have been choosing a new parliament in an election expected to see Prime Minister Abdullah Ahmad Badawi's huge majority reduced.
Inflation, rising crime and ethnic tensions have made inroads into support for his National Front coalition, analysts say.
Mr Badawi called for ethnic minorities to support him.
Some violence linked to the election has been reported in the north-east of the country.
Police in Terennganu State said they had fired tear gas to disperse a crowd of several hundred people protesting at what they saw as vote-rigging.
Arrests
Supporters of the opposition Pan-Malaysian Islamic Party (PAS) stopped buses they suspected of carrying National Front coalition supporters pretending to be voters from the district, said local police chief Ayob Yaacob.
He said 22 people were arrested and the rest of the crowd ran away.
Prime Minister Badawi said before voting began that he did not want a government "made up of only one race" after polls indicated his Chinese and Indian coalition allies might fare badly. Ethnic minorities make up more than a third of the population.
The National Front is still expected to be returned to power by the country's 10.9m eligible voters, as it has at all previous 11 general elections.
Mr Badawi is seeking another five-year term, and he knows that he will get it, the BBC's Robin Brant reports from the capital Kuala Lumpur.
But he has already conceded that he is unlikely to equal the staggering 91% of seats won at the last general election, our correspondent says.
His deputy, Najib Tun Razak, told the BBC that the benchmark for the coalition was a two-thirds majority, giving them power to change the constitution.
`Racial discrimination'
The National Front dominates Malaysian politics and currently controls all but one of Malaysia's 13 states and three federal territories - the northern state of Kelantan, which is held by PAS.
However, analysts say ethnic tensions and widespread concerns about price rises are likely to lead to gains for the opposition parties, including one led by the former Deputy Prime Minister Anwar Ibrahim.
Mr Ibrahim, who is banned from holding office after being jailed for corruption in a trial he says was politically motivated, has promised to end racial discrimination if his Justice Party wins.
"We want strong Malays, strong Chinese, strong Indians," he told a campaign rally on Thursday night.
"Take the best Malays, let them work with the best Chinese and the best Indians."
Many ethnic minorities complain that government policy has denied them fair access to jobs, education, and housing.
Tensions have increased in particular in recent months as a result of a series of illegal street demonstrations. Last November, 10,000 Indians took to the streets during one protest.
Our correspondent says opposition parties put up a strong challenge in certain places, but the overall picture is expected to be much the same as every election since the end of British colonial rule in 1957 once the results are in.
