A total of 19 candidates are vying for the post of president for which voting is taking place across Sri Lanka amid tight security.
Voting began at 7 a.m. and will end at 4 p.m.
In all, according to the Lanka Page web site, some 15 million voters are expected to exercise their franchise at 12,314 polling stations.
Incumbent President Mahinda Rajapaksa is seeking an unprecedented third term, and his challenger, is his former cabinet minister and common opposition candidate, Maithripala Sirisena.
President Rajapaksa is contesting the election from the United People's Freedom Alliance (UPFA) under the symbol of betel leaf, while Sirisena is contesting the poll from the New Democratic Front under the symbol of Swan.
Election Commissioner Mahinda Deshapriya has requested the voters to cast their votes as early as possible and leave the polling center after casting the vote without delay.
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About 25,000 local election monitors and 55 international election observers are monitoring the polls, the web site said in its report.
The Election Secretariat also announced that centers for election complaints will receive complaints or observations.