Alexander Lukashenko was defiant as he voted earlier in the day, warning that the opposition will meet a tough response.
“If you provoke, you will get the same answer,” he said.
“Do you want to try to overthrow the government, break something, wound, offend, and expect me or someone to kneel in front of you and kiss them and the sand onto which you wandered? This will not happen.”
Mindful of Belarus’ long history of violent crackdowns on dissent — protesters were beaten after the 2010 election and six rival candidates arrested, three of whom were imprisoned for years — Tsikhanouskaya called for calm earlier Sunday.
“I hope that everything will be peaceful and that the police will not use force,” she said after voting.
After the polls closed, about 1,000 protesters gathered near the obelisk honoring Minsk as a World War II “hero city”, where police harshly clashed with them, beating some with truncheons and later using flash-bang grenades to try to disperse them.
Some of the protesters later tried to build barricades with trash containers, but police quickly broke them up.
Three journalists from the independent Russian TV station Dozhd were detained after interviewing an opposition figure and were deported.
Tsikhanouskaya emerged as Lukashenko's main opponent after two other aspirants were denied places on the ballot.
Viktor Babariko, head of a major Russia-owned bank, was jailed for charges he called political, and Valery Tsepkalo, an entrepreneur and former ambassador to the United States, fled to Russia with his children after warnings that he would be arrested and his children taken away.