More than 100 black-clad troops armed with clubs poured into the central square at about 3am local time, and loaded demonstrators into waiting vans, leaving behind only the tent camp.
While police had earlier detained some opposition supporters and would-be protesters away from the square, the latest events are the first time demonstrators have been ejected en masse, albeit reportedly without excessive force.
Among those taken away was a son of opposition leader Alexander Milinkevich, according to the opposition leader's wife Inna Kuley.
"Our son is among them and we're going to try to go to where they're being detained," she said, according to an AFP report.
Mr Milinkevich on Thursday warned that increased persecution would only strengthen protests against the authoritarian government.
Last weekend's poll has been widely discredited, with the US and EU denouncing it as undemocratic.
Alexander Kozulin, another opposition candidate at last Sunday's election, arrived quickly at the square after it was cleared and condemned the authorities' actions.
"It's obvious that the authorities' nerve didn't hold -- for them to have sent the police here at night when there were as few witnesses as possible," Mr Kozulin said.
The protest was an unprecedented show of defiance against Mr Lukashenko's leadership, now entering its third term.