Left-leaning former lawyer set to be voted in by electorate galvanised by anger over corruption scandal that brought down Park Geun-hye
South Koreans have gone to the polls to choose a new president after Park Geun-hye was ousted and indicted for corruption, against a backdrop of high tensions with the North.
Voters are galvanised by anger over the sprawling bribery and abuse of power scandal that brought down Park and catalysed frustrations over jobs and slowing growth.
Left-leaning Moon Jae-in, a former human rights lawyer, has held a commanding lead in opinion polls for months. The final Gallup Korea survey of the campaign put him on 38%, ahead of technology entrepreneur Ahn Cheol-soo with 20%.
After casting his vote, Moon said: I feel the peoples strong will to change the government We can make it a reality only when we vote.
Hong Joon-pyo of Parks Liberty Korea party, who the opinion poll had in third place on 16%, out of a field of 13, urged voters to support him and called Moon a pro-Pyongyang leftist.
A record turnout was expected, with 63.7% of voters casting their ballots four hours before the polls closed, compared with 59.3% at the same point five years ago.
Kim Sun-chul, 59, said he voted for Moon because this country needs to restore democracy, which has been so undermined by the Park government.
National elections are public holidays in South Korea and nearly 14,000 voting stations opened at 6am local time on Tuesday (2200 BST on Monday). Exit poll results will be available immediately after voting closes at 8pm.
The campaign has focused largely on the economy, with North Korea less prominent. But after a decade of conservative rule, a Moon victory could lead to a sea change in Seouls approach towards Pyongyang and Washington, a key ally.
Moon, 64, who is accused by his critics of being soft on the North, has advocated dialogue to ease tensions and bring Pyongyang towards negotiations. He is seen as favouring more independence in relations with the US, Seouls security guarantor, which has 28,500 troops in South Korea.
Their presence, he told reporters during the campaign, was important not only to our own security, but also to the global strategy of the US.
Moon has also said he would be willing to visit Pyongyang to meet Kim and advocates the resumption of some of the inter-Korean projects closed by politicians in the South, including the Kaesong industrial zone.
In Seouls prosperous Seocho district, Dr Chung Tae-ean, 72, backed Moons conservative opponent Hong, saying security is the most important thing.
But for many South Korean voters, corruption, slowing growth, unemployment and air pollution from China top the list of concerns.
South Koreas rapid growth from the 1970s-90s pulled the war-ravaged state out of poverty, but the rate slowed as the economy matured. Unemployment among under-30s now stands at a record 10%.
Frustration over widening inequality in wealth and opportunities fuelled anger over the Park scandal, which exposed the cosy and corrupt ties between regulators and chaebols (family owned conglomerates) that have endured for decades.
Park is awaiting trial accused of offering governmental favours to leading businesspeople, including the Samsung heir, Lee Jae-yong, who allegedly bribed her secret confidante Choi Soon-sil.
Moon, Ahn and other candidates have promised to reform the chaebols, which dominate the economy and have long been criticised for operating with little scrutiny.
Another issue is relations with Beijing, which imposed a series of measures seen as economic retaliation over the deployment of the US anti-missile system Thaad in the South.
In an election day editorial, the JoongAng daily said South Korea had been left adrift by the acute division and lack of national leadership stemming from the corruption scandal and Parks impeachment. The vote, it said, was a great opportunity to put the troubled nation back on track.