Some 50,000 people rallied in central Warsaw on Saturday to "defend democracy", denouncing the new conservative government which took office a month ago.

Brandishing Polish and European Union flags and shouting slogans such as "Liberty, Equality, Democracy," the marchers said they felt their basic rights were under threat now.

"It's not Budapest here, it's Warsaw," youth protestors shouted outside the presidential palace, referring to Hungary's populist Prime Minister Viktor Orban, whom critics accuse of stifling human rights and democracy in his country.

The governing Law and Justice (PiS) party won the October general election after eight years in opposition and wasted no time in replacing the heads of the country's secret services.

The eurosceptic party also has plans to overhaul state media and at the moment has the Constitutional Court in its crosshairs.

PiS-backed Andrzej Duda, who was elected in May, maybe president and PiS colleague Beata Szydlo prime minister, but the undisputed boss of Poland's populist, Catholic right is former premier Jaroslaw Kaczynski.

The demonstrators also called for Duda's resignation on the ground that he had violated the constitution.

The Constitutional Court this month found fault with several sections of a law introduced by the PiS in November just three days after its government was sworn in.

The legislation had allowed it to elect five new partisan judges to the Constitutional Court, even though the previous liberal parliament had already approved five new candidates of its own choosing.

Duda swore in the PiS-backed judges in a hasty late-night ceremony. Legal experts have condemned Duda's handling of the saga, accusing the president -- a trained lawyer -- of violating the constitution.

"My freedom and everybody else's freedom is in danger," said Bartosz Kaminski, a man in his forties.

"Communism fell 26 years ago and we thought we would be free ... we have to fight again," he said.

The march was called by a spontaneous civic movement called the Committee for the Defence of Democracy and was attended by the leaders of opposition parties from all hues of the political spectrum.

"I fear that we will become an intolerant country where minorities are oppressed," said 35-year-old trader Karol Katra.

The demonstrators also called for the respect of the constitution and for the indepedendence of the Constitutional Court.

"The majority don't want a dictatorship," said Mateusz Kijowski from the Committee for the Defence of Democracy.