South Koreans went to the polls Wednesday to choose a new president in a close and potentially historic election that could result in Asia's fourth-largest economy getting its first female leader.
Voters face a clear choice between the ruling conservative party candidate Park Geun-Hye and her liberal rival from the main opposition party, Moon Jae-In, with opinion polls unable to separate the two.
The eventual occupant of the presidential Blue House will face numerous challenges, including a belligerent North Korea, a slowing economy and soaring welfare costs in one of the world's most rapidly ageing societies.
Polling booths opened at 6:00 am (2100 GMT Tuesday) and were scheduled to close at 6:00 pm with a national holiday declared to allow maximum turnout among the 40 million-plus registered voters.
Park, 60, is looking to make history by becoming the first female president of a still male-dominated nation, and the first to be related to a former leader.
She is the daughter of one of modern Korea's most polarising figures, the late dictator Park Chung-Hee, who is both admired for dragging the country out of poverty and reviled for his ruthless suppression of dissent during 18 years of autocratic rule.
He was shot dead by his spy chief in 1979. Park's mother had been killed five years earlier by a pro-North Korea gunman aiming for her father.
Moon, who was chief of staff to the late left-wing president Roh Moo-Hyun, is a former human rights lawyer who was once jailed for protesting against the Park Chung-Hee regime.
After locking in the support of their respective conservative and liberal bases, the two candidates put a lot of campaign effort into wooing crucial centrist voters, resulting in significant policy overlap.
Both have talked of "economic democratisation" -- a campaign buzzword about reducing the social disparities caused by rapid economic growth -- and promised to create new jobs and increase welfare spending.
Moon has been more aggressive in his proposals for reining in the power of the giant family-run conglomerates, or "chaebol" that dominate the economy and there are significant differences on North Korea.
While both have signalled a desire for greater engagement with Pyongyang, Park's approach is far more cautious than Moon's promise to resume aid without preconditions and seek an early summit with North Korean leader Kim Jong-Un.
Although North Korea has not been a major campaign issue, its long-range rocket launch last week -- seen by critics as a disguised ballistic missile test -- was a reminder of the unpredictable threat from across the border.
Pyongyang has made no effort to conceal its election preference, having spent months attacking Park's New Frontier Party (NFP) and outgoing President Lee Myung-Bak, whose five-year term was marked by a freeze in inter-Korean contacts.
On Tuesday, North newspapers urged voters to reject the NFP as "a group of gangsters bereft of elementary ethics and morality" and warned that Park was "hell-bent" on confrontation with Pyongyang.
The never-married Park has promised a strong, maternal style of leadership that would steer the country through the challenges of global economic troubles.
"I have no family to take care of and no children to pass wealth to. You, the people, are my family and your happiness is the reason that I stay in politics," Park said in a televised press conference on Tuesday.
"Like a mother who dedicates her life to her family, I will become the president who takes care of the lives of each one of you," she said.
A female president would be a big change for a country that the World Economic Forum recently ranked 108th out of 135 countries in terms of gender equality -- one place below the United Arab Emirates and just above Kuwait.
Moon has stressed the need for a change after what he described as five years of a corrupt and incompetent NFP presidency.
"If you spare them punishment, past wrongs will be extended," he said on the last day of campaigning.
Turnout is expected to be crucial.
Older Koreans, who generally favour Park, are seen as more dependable voters and Moon's camp has pushed hard to ensure the younger demographic that make up his support base actually cast their ballots.