Thailand headed to the polls on Sunday in an election that will test whether one of Asia's most promising nations can end a six-year crisis marked by protests and military crackdowns.

Opinion polls give a clear lead to the opposition Puea Thai (For Thais) party led by Yingluck Shinawatra, 44, a political novice, over British-born, Oxford-educated Prime Minister Abhisit Vejjajiva's Democrat Party.

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

But as Thais began voting, the figure at the heart of the election was not on any ballot and instead living in a luxury villa on another continent in self-appointed exile -- a tycoon-turned politician revered by the poor and loathed by the elite.

Former prime minister Thaksin Shinawatra, Yingluck's elder brother, is not an official candidate but the vote is seen as a referendum on his possible return. From Dubai, he has directed much of his sister's campaign, calling her his 'clone' and helping her rally support in the vote-rich rural heartlands.   

His mostly rural and urban poor red-shirted supporters brought Bangkok's commercial district to a standstill in 11 weeks of protests last year, shuttering five-star hotels before an army crackdown in which 91 people were killed and 2,000 wounded.   

Yingluck has energised the red shirts who rail against the 'double standards' in Thai society, accusing the rich, the establishment and military brass of breaking laws with impunity.

Those grievances have simmered since 2006 coup overthrew her brother, who they idolise as the first politician to address their needs. Yingluck hopes to tap his big base of supporters, a powerful demographic who helped him score landslide election wins in 2001 and 2005.
   
Rallying behind Abhisit are the urban middle classes and the establishment elite in Bangkok, who say Thaksin is an authoritarian crony capitalist, a fugitive from justice and a terrorist who led the red shirts in a wave of violence last year.

They want him to serve a two-year prison term for graft -- charges Thaksin says are politically motivated -- and say a vote for Yingluck is a vote for an amnesty that could pave the way for Thaksin to return.

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

Throughout the six-week campaign, both sides have presented similar populist campaigns of subsidies for the poor, improved health care benefits and infrastructure investment including high-speed rail systems across the country.

But a risk of violence lies in the margin of a Puea Thai win and the reaction of the red shirts. Key as well will be the response of the military, which has a habit of intervening in Thai politics through the coup d'etat. - Reuters