Thailand is voting in a closely fought election that voters hope will end the country's long-running political crisis.

The poll is the first major electoral test for the government since mass opposition rallies in Bangkok last year.

Security is tight for the vote, with around 170,000 police deployed nationwide to protect voting booths.

Dozens of political parties are contesting the ballot, but the front-runners are the ruling Democrats led by incumbent Prime Minister Abhisit Vejjajiva and the opposition Pheu Thai party led by Yingluck Shinawatra, the younger sister of deposed former government leader Thaksin Shinawatra.

Thailand has been deeply divided since the kingdom's military staged a bloodless coup that ousted Thaksin Shinawatra in 2006.

Opinion polls ahead of the vote show Yingluck Shinawatra ahead of the prime minister, but analysts say the opposition leader's personal popularity does not guarantee her a parliamentary majority.

These elections will be the nation's first since anti-government protests by the former prime minister's supporters last year led to clashes in which more than 90 people died.

On Saturday, a car bomb exploded in southern Thailand's Narathiwat province.

Violent incidents are common in much of southern Thailand, which has a large Muslim population. Most attacks have been attributed to radical groups trying to break away from the majority-Buddhist nation.