PRAGUE - Around a quarter-million Czechs flooded central Prague on Saturday to mark 30 years since the Velvet Revolution toppled communism in then-Czechoslovakia, with protesters demanding that billionaire Prime Minister Andrej Babis quit over allegations of graft.

Some demonstrators waved flags or brandished banners calling for Babis to step down and chanted "Shame!" and "Resign!".

The CTK Czech news agency quoted Interior Minister Jan Hamacek as saying some 250,000 people had rallied at Letna park -- the site of some of the biggest 1989 rallies -- matching a similar protest in June.

It came on the eve of the 30th anniversary of the Velvet Revolution, which saw unprecedented protests and a general strike end four decades of Soviet-imposed totalitarianism in the former Czechoslovakia.

A former communist, the populist Babis faces a string of graft allegations and a conflict-of-interest probe by the European Commission centered on Agrofert, his sprawling farming, media and chemicals holding.

Babis has denied any wrongdoing and his ANO (YES) party still tops opinion polls with around 30 percent support despite the controversy.

He is also tagged as an agent in secret police files from the 1980s, something he has vociferously denied.

People living in a house overlooking the rally strung a banner saying "Truth and love must prevail over lies and hatred", the motto of former Czech President Vaclav Havel, a former anti-communist dissident playwright.

Kristyna Kovarova, a 20-year-old student from the southern village of Malenice, said she had come "to fight for democracy."

"I think democracy is in danger because there are many people trying to twist it and set their own rules, but that's not right," she told AFP.

"I really don't like our prime minister's lies," said protester Josef Plandor, who traveled from the eastern village of Zasova.

"His huge conflict of interest, his lies, fraud, there's too much of that. He's not an honest man," said the 43-year-old forestry worker, adding that he was "sure" Babis would never quit.

The Million Moments for Democracy movement, which organized the protest, called on Babis to either resolve his conflict of interest or step down.

The 65-year-old Slovak-born politician was charged last year in connection with a two million euro EU subsidy scam, but in September a Prague prosecutor cleared him. -AFP