Sri Lankans are voting in the country's first national election since the end of a 25-year conflict in May.
President Mahinda Rajapaksa and General Sarath Fonseka are two former allies who lay claim to the victory over the Liberation Tigers of Tamil Eelam (LTTE) and are vying to rebuild a nation without conflict.
Gen Fonseka is unable to vote because his name is not on the electoral register.
More than 14m people are registered to vote, against a backdrop of heavy security and tension.
Some 68,000 police and 250,000 election officials have spread out across the Indian Ocean island.
There are fears that election day will be as bloody as a campaign in which five people were killed and more than 800 violent incidents were recorded.
Before polls opened, loud blasts were heard in the northern city of Jaffna, the centre of Sri Lanka's minority Tamil culture that has been under military guard since 1995.
There are no reports of injuries and it was not immediately clear what caused the explosions.
President Rajapaksa and General Fonseka are the surprising rivals in a contest in which the defeat of the Tamil Tigers in May has figured heavily in campaigning, with both claiming credit.
'Today's victory will be remarkable. It's been evident with voters across the nation participating towards our victory,' Mr Rajapaksa said after voting in Medamulana, his rural district on the southern coast.
'We expect a peaceful election and are getting ready to enjoy a better tomorrow.'
Mr Rajapaksa and Gen Fonseka have both pledged to dole out costly subsidies and public sector pay rises.
Economists say it will be hard for Sri Lanka to meet its cost-cutting obligations under a $2.6bn International Monetary Fund loan.
