Belarus opposition leader Svetlana Tikhanovskaya said supporters launched Monday a nationwide strike after her deadline expired for strongman Alexander Lukashenko to step down.
"Today the People's Strike is beginning," Tikhanovskaya said on her Telegram channel.
"Employees of state factories and enterprises, transport workers and miners, teachers and students have gone on strike since this morning."
All major stores and pharmacies were open in the capital Minsk on Monday but some small business were shuttered, an AFP reporter said.
Several thousand pensioners and students took to the streets of Minsk to back the workers.
"We want to live in a free democratic country, we should defend those who have been beaten up," student Ivan Prokhorov told AFP at the protest.
Tikhanovskaya had given Lukashenko until Sunday to quit, halt violence against protesters and release political prisoners, warning he would otherwise face a general strike from Monday.
The 66-year-old Lukashenko, accused by the opposition of stealing August polls, ignored the ultimatum and police cracked down on the latest of a series of opposition protests on Sunday.
Tikhanovskaya praised the "incredible level of solidarity" among Belarusians and pledged the strikes would continue.
Speaking on YouTube, she said that over $7 million have been raised in support of the strikers.
The 38-year-old opposition figure, who claims to have won the August 9 election and is now based in EU member Lithuania, did not provide any figures on the number of people participating.
Independent reporting inside Belarus has been curtailed and it was not possible to immediately estimate the scale of the action.
Citing witnesses, local news outlet Onliner said police deployed patrol vans and other vehicles outside major plants including Grodno Azot chemicals, the Minsk Automobile Plant and Minsk Tractor Works.
Rights group Viasna reported more than 170 people had been detained in Minsk and other cities on Monday.
'Thousands like me'
Elena Velichko, who works in the beauty industry, said she did not go to work on Monday in support of the strike.
"There are thousands of people like me," the 43-year-old told AFP near a Minsk department store where more than a dozen protesters had formed a human chain.
Natalya Bezrukova, 54, said she and several co-workers also went on strike from their jobs at a state construction company.
"We are against the Lukashenko regime. We don't need any deaths or murders or repression. We want to live in a free democratic country," she said.
Authorities denied the strike call was being followed, with government spokeswoman Alexandra Isaeva saying that on Monday morning all companies were "operating in routine mode".
Alexander Yaroshuk, head of the Belarusian Confederation of Democratic Trade Unions, said he was aware that some unions and individual workers were ready to strike.
"But it's hard to predict just how far people will go given the authorities' massive pressure," Yaroshuk told AFP.
The ex-Soviet nation has been gripped by historic protests since Lukashenko claimed election victory over Tikhanovskaya, a political newcomer, who ran after her blogger husband was jailed and prevented from joining the race.
The protest movement has kept up large-scale demonstrations for the past two months, with tens of thousands taking to the streets every Sunday.
More than 500 people were detained at protests in Minsk and other cities on Sunday, the interior ministry said.
Several people died and thousands were arrested in a post-election crackdown, with harrowing accounts emerging of abuse in jails.