Late on Saturday, the government pledged to repeal a decree widely seen as easing the penalties for corruption that sparked days of furious protests, saying it would meet to do so on Sunday.
But demonstrators were not convinced.
"Today we are going to break new records," Florian, 40, told AFP in Bucharest, saying he didn't trust the government to retract the legislation as promised.
"We don't believe that," the electrician said as he distributed free pretzels and tea at Victory Square, the epicentre of this week's protests.
By midday (1000 GMT) on Sunday, several hundred people could be seen gathering in the square but the crowd was expected to swell with thousands arriving on buses from outside the capital.
On Saturday, an estimated 330,000 people demonstrated across the nation, TV reports said, in what was the biggest turnout since the toppling of dictator Nicolae Ceausescu in 1989.
The crowds, largely young, have chanted, waved banners, blown vuvuzela horns in the national colours and paraded effigies of government officials in black-and-white prison uniforms.
Critics say that the emergency government decree issued late on Tuesday represents a retreat on corruption, long the scourge of this ex-communist nation.
The government said it would align the penal code with the constitution but protesters saw it as a brazenly transparent attempt by the ruling Social Democrats (PSD) to let off many of its own officials and lawmakers.
In addition, the government, in office for barely a month, wants to release some 2,500 prisoners serving sentences less than five years, ostensibly to reduce overcrowding in jails.
In recent years Romania, a European Union member since 2007, has won praise for its considerable progress tackling graft, but Tuesday's decree sparked a chorus of alarm from both Washington and Brussels.
'Must stay vigilant'
On Saturday evening as the crowds swelled, Prime Minister Sorin Grindeanu finally announced the climbdown, saying the government would meet Sunday to repeal the decree.
"I do not want to divide Romania," a pale and tired-looking Grindeanu said in a televised address, sparking cheers and celebrations late into the night from protestors outside.
But he said the government still needed to bring laws into line with the constitution, slamming what he called a campaign of misinformation and "distortion".
Raluca, a demonstrator in her 30s, said she was delighted but that the government was still not to be trusted.
"People are going to remain very vigilant with this government," she told AFP late Saturday.
Her words were echoed on Sunday morning by Rado, one of a sweaty trio cycling on bikes fixed to the ground at Victory Square, who said he was "sick" of corruption.
"Usually we do a Sunday trip, we cycle around 100-150 kilometres (60-90 miles)," said the 27-year-old who works for an online sports shop.
"And since we have to look out for the thieves in our government, we decided just to come here and train," he told AFP.
"We just want someone competent to run the state for the people. Not for themselves, for their own benefit and bank accounts."
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