President Milos Zeman, 73, is seeking another five-year term in the largely ceremonial post and is the favorite to win the election's first-round vote Friday and Saturday.
Two political newcomers, the former president of the Academy of Sciences, Jiri Drahos, and popular song writer Michal Horacek are considered his major challengers. Others with a chance to advance to the runoff are Mirek Topolanek, an outspoken leader who served as prime minister from 2006 to 2009, and Pavel Fischer, a former diplomat.
If no candidate achieves a majority, the top two will face each other in a runoff in two weeks.
Friday's vote was hit by a protest. After Zeman entered a polling station in Prague, he was approached by a female Femen activist stripped to the waist who shouted "Zeman, Putin's slut!" His guards intervened and led the shaken president away. Zeman returned several minutes later to vote and said he was honored to be heckled by a Femen activist.
Zeman was elected to the largely ceremonial post in 2013 during the country's first direct presidential vote, a victory that returned the former left-leaning prime minister to power.
In office, he's become known for strong anti-migrant rhetoric that won him support from the populist far-right. He has also divided the nation with his pro-Russia stance and his support for closer ties with China.
He was one of the few European leaders to endorse Donald Trump's bid for the White House. He has flown the European Union flag at Prague Castle but has used every opportunity to attack the 28-nation bloc.
Copyright 2018 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.