According to the sources, Correspondents in the city said more than thousands filled the central square despite a tougher police presence.
The protesters are insisting Mr Lukashenko stole the election and demanding his resignation.
The president has sworn to crush unrest and blamed the dissent on unnamed “foreign-backed revolutionaries”.
Recent protests were met with a crackdown in which at least four people were killed. Demonstrators said they had been tortured in prisons.
According to official results, Mr Lukashenko – who has ruled Belarus for 26 years – won more than 80% of the vote in the 9 August election and opposition leader Svetlana Tikhanovskaya 10%.
There were no independent observers and the opposition alleges massive vote rigging.
Ms Tikhanovskaya, who was forced to flee to neighbouring Lithuania the day after the election, vowed to “stand till the end” in the protests.
‘If you croak we don’t care’: Brutality in Belarus ‘There’s no way back. The people will not forgive this’ What is happening in Minsk? Tens of thousands of people – from the elderly to those with small children – poured into Independence Square on Sunday.
Many were carrying the opposition’s red and white flags, and chanted “freedom” and anti-government slogans.
Pro-opposition media put the crowd at more than 100,000.
After gathering in the square, some demonstrators moved towards the “Hero City” war memorial and the presidential palace, where they were blocked by a security cordon.
State television later released a video showing Mr Lukashenko arriving at the presidential palace by helicopter, wearing a flak jacket and carrying an automatic weapon.
Meanwhile in Lithuania, thousands of people – including President Gitanas Nausėda – formed a human chain from the capital Vilnius to the Belarusian border in solidarity with those protesting in Minsk.
More human chains were planned in the Estonian capital Tallinn and in Prague in the Czech Republic.
This weekend’s rally in Minsk follows the country’s biggest protest in modern history last Sunday, when hundreds of thousands filled the streets. Strike action in key factories across Belarus is also keeping up the pressure on the president.
Video captionWhat lies behind the Belarus protests?
Losing fear Analysis by Jonah Fisher, BBC News, Minsk. This was another massive demonstration carried out under the noses of Alexander Lukashenko’s security forces.
Belarus’s beleaguered president had instructed his interior ministry to end the “unrest” and promised to “solve the problem”. But in the end no serious effort was made to stop protesters gathering.
In the back streets leading into Independence Square there were long lines of riot police and army trucks. They looked on as the swelling crowd ignored loudspeaker warnings that this was an illegal gathering and to disperse.
These demonstrations are organic and loosely organised, so in the square there is no stage or PA system. That means no place for the few opposition leaders that remain free in Belarus to make speeches.
Instead the protesters marched around chanting “Long live Belarus” and “Go Away Lukashenko” before heading off towards a war memorial. Some told me that they had been scared to come but now felt safe surrounded by so many like-minded Belarusians.
What has Lukashenko said? The 65-year-old president insists he won the election fairly and has ruled holding another poll. On Saturday he accused Nato of “trying to topple the authorities” and install a new president in Minsk.
He said he was moving troops to the country’s western borders to counter a Nato build-up in Poland and Lithuania, and vowed to “defend the territorial integrity of our country”.
Nato responded by saying it posed “no threat to Belarus or any other country” , and had “no military build-up in the region”.
“The regime is trying to divert attention from Belarus’s internal problems at any cost with totally baseless statements about imaginary external threats,” Lithuanian President Gitanas Nauseda told AFP news agency on Saturday.
Mr Lukashenko has also accused an opposition council – set up by Ms Tikhanovskaya to organise peaceful transition – of trying to seize power. Two of its members were questioned by police on Friday.
Belarus – the basic facts Where is Belarus? It has Russia – the former dominant power – to the east and Ukraine to the south. To the north and west lie EU and Nato members Latvia, Lithuania and Poland.
Why does it matter? Like Ukraine, this nation of 9.5 million is caught in rivalry between the West and Russia. President Lukashenko, an ally of Russia, has been referred to as “Europe’s last dictator”. He has been in power for 26 years, keeping much of the economy in state hands, and using censorship and police crackdowns against opponents.
What’s going on there? Now there is a huge opposition movement, demanding new, democratic leadership and economic reform. Mr Lukashenko’s supporters say his toughness has kept the country stable. News source is from BBC