Sunday’s demonstration overflowed Minsk’s sprawling 17-acre Independence Square.
There were no official figures on crowd size, but it appeared to be 150,000 people or more.
The demonstrators then marched to another square about one-and-a-half miles away.
Police made no immediate efforts to break up Sunday’s protest.
Protesters say the official August 9 presidential election results that gave President Alexander Lukashenko a sixth term in a landslide are fraudulent.
The size and duration of the protests are unprecedented for Belarus, a former Soviet republic of 9.5 million people.
Video from Belarus on Sunday showed the beleaguered president carrying a rifle and wearing a bulletproof vest as he got off a helicopter that brought him to his working residence amid the 15th straight day of protests.
As Mr Lukashenko landed at the Independence Palace in Minsk, protesters were gathered in a nearby square.
The video was released on the Telegram messaging app on a channel that other media identified as being close to Mr Lukashenko’s press service.
The 65-year-old leader – who has been in power for 26 years – appears to be flailing about for a strategy to counter them.
He has repeatedly blamed Western interference, claimed the protests were backed by the United States and accuses Nato of building up troop concentrations in Poland and Lithuania on Belarus’ western border, which the alliance denies.
He also claimed that Russian president Vladimir Putin was willing to offer security assistance to his government to quell the protests if he asked for it.
A similarly enormous crowd turned out for a protest a week ago and daily demonstrations have taken place since the vote.
Several of the country’s key factories have been hit with protest strikes by workers fed up with government policies.
Those strikes not only threaten the already-ailing economy, but show that opposition to Mr Lukashenko extends beyond educated white-collar circles and into his traditional blue-collar base.
“Belarus has changed. Lukashenko has been able to unify everybody, from workers to intelligentsia, in the demand for change,” said protester Slava Chirkov, who attended Sunday’s demonstration with his wife and son.
They held a sign declaring “Lukashenko, your milk has gone sour”, referencing Mr Lukashenko’s former job as the director of a Soviet-era collective farm.
Mr Lukashenko’s main election challenger, Sviatlana Tsikhanouskaya, fled to Lithuania the day after the election.
Several other possible challengers fled the country even before the election.
An opposition Coordination Council was created last week to develop a strategy for a transition of power, but authorities in Belarus have opened a criminal probe into its formation.
