Polls opened early Wednesday morning in South Korea's closely contested presidential election, which pits the daughter of a military strongman against a former human rights lawyer once jailed for protesting his rule.

Voting began at 6:00 a.m. local time at 13,542 polling stations nationwide, with more than 40.4 million eligible voters poised to cast their ballots. Polls close at 6:00 p.m., and the result is expected by midnight.

Opinion surveys released last week showed Park Geun-hye of the conservative ruling Saenuri Party held a slight lead over her liberal rival, Moon Jae-in of the center-left main opposition Democratic United Party.

Still, the gap in most polls was within the margin of error, and analysts say the contest is too close to call and its outcome will ultimately depend on voter turnout.

Park, the 60-year-old daughter of South Korean dictator Park Chung-hee, is looking to become the first female leader of the country and extend the conservative rule for another five years.

"I will restore the middle class and expand it to 70 percent of the country," Park said Tuesday during a press conference in her campaign headquarters in Seoul.

Park, who acted as the de facto first lady to her father after her mother was assassinated, remains popular among older voters nostalgic for the rapid economic growth under the 18-year authoritarian rule.

She is an anathema, however, to former democracy activists such as Moon, who was jailed in 1975 for protesting against the late dictator.

Moon, 59, is a former human rights lawyer who also served as chief of staff to late President Roh Moo-hyun. He believes that the election is a contest between vested interests and aspirations for new politics.

"It has been proved that the Saenuri Party is incapable of representing the country," Moon said on the last day of campaigning.

He is the sole candidate running on the liberal ticket after independent Ahn Cheol-soo and leftist candidate Lee Jung-hee bowed out of the race to throw their support behind him.

Incumbent President Lee Myung-bak, whose single five-year term ends early next year, is constitutionally barred from seeking re- election.