South Koreans head to the polls to vote for a new president, in what's become a tight race to lead the country.

The election pits Park Geun-hye, the daughter of a former military ruler, against Moon Jae-in, a man jailed for political activism under Park's father.

Park, who cast her ballot in Seoul, is running as the ruling party candidate.

She has a narrow lead in polls and will become South Korea's first female leader if voting goes her way.

But she faces fierce competition from her left-of-centre rival.

Moon is a former human rights lawyer, who's urged disillusioned South Koreans to vote for change.

Analysts expect a close result for the front-runners, who are separated by just 0.5 percent in some polls.

Just an hour after polling opened and more than 1.1 million people had already cast votes.

Exit polls will be announced later this evening as the ballot closes at 6 p.m local time (0900 GMT).