Former defence secretary Gotabaya Rajapaksa, who oversaw the military defeat of Tamil separatists 10 years ago, and government minister Sajith Premadasa are locked in a close fight, politicians and analysts say.

Rajapaksa has vowed to overhaul national security, playing on the fears of the majority Sinhalese Buddhists following the April attacks claimed by Islamic State that killed more than 250 people.

Premadasa has sought to fire up the countryside with promises of free housing, school uniforms for students and sanitary pads for women - touching on a topic rarely discussed in public anywhere in south Asia but which has drawn women to his rallies.

Police said a group of unidentified men opened fire on buses carrying Muslims to a polling station in Anuradhapura district in central Sri Lanka. There were no injuries but witnesses said there were tires burning.

At a polling station in Colombo, M. Gunasekera, a 41-year-old homemaker, said the most important problem was widespread corruption and the lack of accountability of politicians.

About 16 million people are eligible to vote, with the ballot allowing voters to choose up to three candidates in order of preference.

Votes will be counted soon after polling stations close but the results are not expected before Sunday.

Muslims who make up nearly 10 percent of Sri Lankaa's 22 million population, say they have faced hostility ever since the April attacks.

That division has come on top of long-standing grievances of ethnic Tamils, who say they are still to get justice stemming from the human rights violations during a 26-war civil war with Tamil rebels that ended in 2009.

REUTERS