South Koreans are voting in a presidential election, called early after a huge corruption scandal brought down their former leader.
Liberal Moon Jae-in is the clear front-runner with centrist Ahn Cheol-soo his nearest challenger.
The election is being closely watched at a time of economic uncertainty and heightened tensions with North Korea.
Mr Moon wants to increase contact with the North in contrast to ex-leader Park Geun-hye who cut almost all ties.
Observers are expecting a high turnout at the ballot boxes, with numbers boosted by younger voters, as South Koreans choose from 13 candidates.
Polls close at 20:00 local time (11:00 GMT), with the winner expected to be announced soon after.
Money and jobs
All the candidates are promising to protect the fragile recovery in South Korea’s economy – the fourth largest in Asia – and to bring down youth unemployment, which remains stubbornly high.
There are also promises to rein in perceptions of elitism in South Korean political society and reform the family-run conglomerates – chaebols – which dominate the domestic economy.