Bangkok: Thailand began voting on Sunday in a closely fought general election seen as a major test of the kingdom's ability to resolve a long and bloody political crisis.

Polling stations opened at 8:00 am (0100 GMT) amid a heavy police presence for the vote, the first since mass anti-government protests in Bangkok last year sparked the country's deadliest political violence in decades.

The election will test whether one of Asia's most promising nations can end a six-year crisis marked by bloody protests, military crackdowns and growing tension between rich and poor.

Thailand's first woman prime minister

Opinion polls give a firm lead to the opposition Puea Thai (For Thais) party led by Yingluck Shinawatra over Prime Minister Abhisit Vejjajiva's Democrat Party, but it is less clear she will win by enough votes to form a government.

"Thank you, supporters who have been so kind to me," Yingluck, who could become Thailand's first woman prime minister, said outside a polling booth in Bangkok.

Yingluck's elder borther in exile

But as Thais voted, the figure at the heart of the election was in self-imposed exile in another region. Former Prime Minister Thaksin Shinawatra, Yingluck's elder borther, is not on any ballot but the vote is seen as a referendum on his return.

From Dubai, he has helped direct his sister's campaign, calling her his "clone" -- a comment that resonates in the vote-rich heartlands, where he is idolised as the first politician to pay attention to the needs of millions living outside Bangkok.

"I want peace. I want a change in Thailand," said Suwanee Thila, a government worker and red-shirt supporter in Ban Sampran, a village outside Udon Thani in Thailand's northeast.

Red shirts

The red shirts have rallied around Yingluck and accuse Abhisit of colluding with the army to rule with impunity, grievances that have simmered since a 2006 military coup overthrew her brother.

Thaksin, a former telecommunications tycoon, scored landslide election wins in 2001 and 2005 by appealing to the poor with a trove of populist policies, from cheap credit to universal healthcare. Yingluck hopes to tap his supporters.

"The Land of Smiles"

In the balance is Thailand's reputation as "The Land of Smiles", an image that collapsed last year amid scenes of horror: military snipers firing on demonstrators, mysterious black-clad gunmen rallying behind protesters, banks on fire and grenades exploding in the business district.

Abhisit, 46, an urbane economist born in Britain and educated at Oxford, has warned that Thailand could return to instability if Yingluck wins. He blames the red shirts for the violence and casts Thaksin as an authoritarian crony capitalist and fugitive.

"Voters do not want a government to come in and whitewash corruption charges. We have to believe in the court system," Korbsak Sabhavasu, chairman of the Democrat Party's strategy team, said before the vote.

The polls close at 3 p.m. (0800 GMT) and the first indication of the winner could come within an hour. The official result is expected late in the evening.