Voting which started at 7 a.m. at 12,845 polling centres island-wide, will end at 5 p.m., reports the Daily Mirror newspaper.
A total of 15,992,096 Sri Lankans are eligible to cast their ballots in a contest that will witness a battle between a record 35 candidates.
This is the highest number of contenders since the first presidential election which was held in 1982, and up from 18 candidates who contested the last one in 2015.
An Election Commission (EC) official said that the results were expected by Saturday night.
"We cannot tell the exact time. But, it will be midnight. It all depends on the efficiency of officials on election duty and counting," the Daily Mirror quoted the official as saying.
Although there are 35 candidates in the fray, it appears that only Sajith Premadasa (52) from the ruling New Democratic Front (NDF) alliance and the the Sri Lanka Podujana Peramuna's (SLPP) Gotabaya Rajapaksa (70) are the main contenders for the country's highest office, Efe news reported.
Gotabaya is a retired soldier who took over Sri Lanka's defence portfolio during the period when his older brother, Mahinda Rajapaksa was President (2005-2015) and also when Sri Lanka ended its war in 2009 with the Liberation Tigers of Tamil Eelam (LTTE).
While the family's political future appeared to be fading after Mahinda's defeat in the 2015 presidential election, the April 21 Easter bombings on churches and luxury hotels - in which 269 people lost their lives - lent wings to Gotabaya's candidacy.
He has presented himself during the presidential campaign as a nationalist and champion of the Sinhalese Buddhist majority, while promising strong national security in the wake of the April attacks.
On the other hand, questions about whether he gave up his US citizenship before filing his nomination have sparked controversy over the legality of his candidature.
Meanwhile, Sajith Premadasa is the son of Ranasinghe Premadasa, who served as the President from 1989 until he was assassinated in May 1993 in Colombo in a suicide bombing by the LTTE.
The Minister of Housing and Construction is seen as the most likely contender to defeat Gotabaya, and has pledged to fight for the Muslim and Tamil minorities, who believe him coming to power could help safeguard their rights.
The votes from minority Tamils and Muslims had also played a major role in the election of incumbent President Maithripala Sirisena in January 2015.
The other main candidates are Anura Kumara Dissanayake leader of the Marxist party, Janatha Vimukthi Peramuna (JVP), which led to youth insurrections in 1971 and 1987-1988.
The fourth popular contender is former Army Commander Lt. Gen. Mahesh Senanayake who formed National People's Party (NPP) after he left the army last August. He led the army in the aftermath of the Easter Sunday attacks in flushing out radicals.
If Premadasa wins the election, the present cabinet and government would continue until the next general election to elect lawmakers.
And if Gotabaya Rajapaksa manages to win and proves 113 majority power in Parliament, there is a possibility of a change of government.
( With inputs from IANS )