Protests also took place in nine other cities, underlining the wide extent of dismay and anger with President Alexander Lukashenko, who has stifled opposition and independent news media during his 26 years in power.
The protest wave began after the August 9 presidential election that officials said gave Mr Lukashenko a sixth term in office with a crushing 80% of the vote. The opposition and some poll workers say the results were manipulated.
Mr Lukashenko has defied calls for him to step down and many prominent members of a council formed with the aim of arranging a transfer of power have been arrested or have fled the country. The protests have persisted despite the daily detentions of demonstrators.
The Interior Ministry said that about 200 demonstrators were arrested throughout the country on Sunday.
Police and troops blocked off the centre of Minsk with armoured vehicles and water cannons.
Mr Luksahenko stepped up his defiance this week by unexpectedly taking the oath of office for a new term in an unannounced ceremony, leading many to mock him as harbouring royal-like pretensions.
Some of the estimated 100,000 people who braved rain and strong winds to march in a two-kilometre-long (mile-long) column wore crowns made of cardboard and bore placards calling Mr Luksahenko “the naked king”.
Lukashenko’s main election opponent, Sviatlana Tsikhanouskaya, praised protesters’ determination and urged them not to let their energies flag.
“Today is the 50th day of our protest and the Belarusian people have again come out on the streets,” she said in a statement from Lithuania, where she went into exile after the election.
“We have come to stop this regime and we will do this peacefully.
“Democracy is the power of the people. The entire people are stronger than one man.”
Western countries have widely denounced the dubious election and the crackdown on protesters. The European Union and the United States are considering sanctions against Belarusian officials.
Foreign minister Vladimir Makei told the UN General Assembly on Saturday that these expressions of concern are “nothing but attempts to bring chaos and anarchy to our country”.
