Voters in Thailand are heading to the polls for the country's first general election in four years. Observers are waiting to see whether the military-linked government will be able to hold onto power. It took control in a coup nine years ago.

Prime Minister Prayut Chan-o-cha led the coup. He is seeking re-election with the backing of the United Thai Nation Party.

But the largest opposition Pheu Thai Party has topped the latest opinion polls with a support rate of nearly 40 percent. The PTP is affiliated with former Prime Minister Thaksin Shinawatra. He was ousted in a prior coup in 2006.

The PTP's prime ministerial candidate is Thaksin's daughter, Paetongtarn.

Another opposition contender is the Move Forward Party. It ranked second in the opinion polls. The party managed to rapidly expand its support among young voters during the final days of campaigning.

The 500-member lower house of parliament and the military-appointed senate will vote jointly to select the next prime minister. That will happen after voters cast their ballots. An opposition party will have to win an overwhelming majority in the election to bring about a change of government.

Voting stations will close at 5 p.m. on Sunday. Ballot counting will begin afterwards. Preliminary results are expected by the end of the day.