|Taib Mahmud, who has ruled Sarawak for 30 years, is in the centre of a series of corruption scandals [Reuters]
Voting is under way in a key Malaysian state poll widely seen as a test for early general election which is not due until 2013.
Hundreds of thousands of voters cast ballots on Saturday in a vote that will test the ruling coalition's ability to block the opposition's hope of wrestling national political power.
Najib Abdul Razak, the Malaysian prime minister, and other senior government politicians have spent the past week campaigning in coastal towns and villages deep in Borneo's rainforest.
The ruling Barisan Nasional (National Front) party is trying to retain control of a 71-seat legislature in the eastern Malaysian state.
The Barisan Nasional previously held 63 seats and is widely expected to win this election.
Polls will close at 5pm local time (09:00 GMT) with final results expected by 11pm (15:00 GMT).
A strong win for the ruling coalition in the sprawling, resource-rich state of Sarawak on Borneo island could prompt Najib to call a national election this year.
The opposition has been hampered by a lack of resources to reach indigenous tribal communities in remote districts accessible only by boat or helicopter.
"This election is different and for the National Front, tougher. It is certainly the most exciting state election and some would say the most unpredictable," the government-controlled New Straits Times newspaper said in an editorial on Saturday.
"While the National Front is bullish, albeit with some losses, the opposition also is looking at better results."
Najib has pledged huge sums of money in development aid to build new roads and improve facilities in Sarawak, which is rich in timber but comprises many poor communities with little access to electricity and modern communications.
"Don't vote based on sentiments," Najib said late on Friday. "The question that needs to be thought over by Sarawak voters is ... a better future, because Sarawak is a very big state that needs huge investments, particularly in modern infrastructure."
"We want to deny [the government] its monopoly of Sarawak"
Anwar Ibrahim, parliamentary opposition leader, Malaysia
The three-party opposition alliance led by Anwar Ibrahim hopes to seize one-third of Sarawak's legislature seats, mainly in urban constituencies, amid public dissatisfaction over alleged corruption and the slow rate of development in the state.
In the state capital of Kuching, the opposition held its final rallies on Friday night which drew more than 10,000 supporters. The party's election candidates addressed the mainly ethnic Chinese crowd in Mandarin, and were greeted with shouts of "Ubah!" (change).
The opposition is banking on voter frustration over the 30-year rule of Taib Mahmud, the state's chief minister whom critics say has amassed huge riches through shady timber deals, including real prime estate abroad.
"We want to deny [the government] its monopoly of Sarawak," Anwar said.
Taib has denied any wrongdoing, but promised recently to step down within a few years.
The Sarawak state election is Malaysia's biggest since 2008 national polls, when the opposition alliance won more than one-third of the seats in parliament amid complaints of racial discrimination and economic mismanagement by the government.