South Koreans headed to voting stations on Tuesday to elect a new leader, looking to move on from a corruption scandal that brought down former President Park Geun-hye and shook the political and business elite to the core.
Unless there is a major upset, liberal Moon Jae-in - who calls for a moderate approach on North Korea, wants to reform powerful family-run conglomerates and boost fiscal spending to create jobs - will be elected president.
The vote will end a months-long leadership vacuum. Park was ousted on charges of bribery and abuse of power in March to become South Korea's first democratically elected president to be forced from office. She is in jail, on trial.
Park has denied wrongdoing. She decided not to vote, despite having the right to do so, South Korean media reported.
Moon, who narrowly lost to Park in the previous presidential election in 2012, has criticised the two former conservative governments for failing to stop North Korea's weapons development. He advocates a two-track policy of dialogue while maintaining pressure and sanctions to encourage change.
A Gallup Korea poll published last Wednesday showed Moon with 38 percent support in a field of 13 candidates, with centrist Ahn Cheol-soo his nearest challenger on 20 percent.
Moon told reporters after casting his ballot he had "given the campaign his all," and urged South Koreans to vote.
Ahn, who voted earlier at a different polling station, said he would wait for the people's "wise decision". Other presidential candidates were also seen voting early in the day.
Voter turnout stood at 19.4 percent by 11 a.m. (0200 GMT Monday), according to the National Election Commission (NEC), lagging the 26.4 percent turnout seen at the same hour in the 2012 election.
The NEC forecasts total voter turnout reaching more than 80 percent, which would be the highest since President Kim Dae-jung was elected in 1997 after 80.7 percent of eligible voters cast ballots.
One in every four voters cast ballots in early voting last week, seen driven by higher participation by younger people.
The polls opened at 6 a.m. (2100 GMT on Monday) and will close at 8 p.m. (1100 GMT).
A Moon victory would provide much-needed stability and was expected to improve market sentiment at a time when robust exports have supported a recovery in Asia's fourth-largest economy.
The won is up nearly 7 percent against the dollar this year, while South Korean shares are trading at a record high with foreign investors confident about corporate earnings after South Korean businesses did well in the first quarter.
South Korean financial markets are closed on Tuesday but will resume trade on Wednesday.
The winner is expected to be sworn in on Wednesday, after the NEC releases the official result. Most candidates, including Moon and Ahn, plan to skip a lavish inauguration ceremony if successful and start their new job right away.
The new leader is expected to quickly name a prime minister, who will need parliamentary approval, and main cabinet positions, including national security and finance ministers, which do not need parliamentary confirmation.
'New era'
The election is being watched closely by allies and neighbors at a time of high tension over North Korea's accelerating development of weapons. Pyongyang carried out its fifth nuclear test in September and is believed ready for another.
The new president will also face the challenge of defusing tension with China, which is angry about South Korea's decision to deploy a U.S. THAAD anti-missile defence system that China sees as a threat.
"It would be advisable that the next South Korean leader respond positively to China's proposal to resume dialogues - Pyongyang suspends its nuclear program in exchange for the U.S.-South Korean halt of military exercises - something the previous South Korean leaders have failed to do in the past 10 years," a commentary in China's official Xinhua news agency said on Tuesday.
"Moreover, to demonstrate its readiness to ease tensions, Seoul should also call off deploying the THAAD system, which has proved useless in thwarting Pyongyang's nuclear and missile activities," it said.
U.S. President Donald Trump has vowed to stop North Korea developing a nuclear missile that can hit the United States.
North Korea would be keen to see a Moon victory. Its official Rodong Sinmun newspaper said in a commentary on Tuesday conservative rule in the South should be "buried in the grave of history."
"Cleanly eradicating the puppet conservative group that has committed intolerable crimes is the shortcut to new politics, new life and a new world," it said.
The U.S. State Department said Washington looked forward to continuing "close, constructive, deep cooperation" with South Korea's new president.
"We will continue to meet all our alliance commitments, especially with respect to defending against the threat from North Korea," State Department spokeswoman Katina Adams told Yonhap News Agency on Monday.