A mayor in Brussels on Tuesday sent police officers to break up a gathering of prominent, self-described “anti-woke” conservatives from across Europe, including Prime Minister Viktor Orban of Hungary, declaring “the far-right is not welcome” before the authorities quickly retreated.

Emir Kir, the Socialist Party mayor of the central Brussels neighborhood where the gathering took place, issued the order to close the National Conservatism Conference on grounds of “public safety.” But critics said that Mr. Kir’s order only amplified one of the gathering’s main themes: that cancel culture targeting conservative voices has run amok.

“This is what we are up against. We are up against an evil ideology. We are up against a new form of communism,” declared Nigel Farage of Britain. Mr. Farage, a former member of the European Parliament and a champion of national sovereignty, who helped drive his country’s exit from the European Union, was getting ready to speak when the authorities arrived. “This is like the old Soviet Union. No alternative view allowed,” he said.

A small group of Belgian police officers entered the conference venue but then quickly withdrew after telling organizers that their event had been prohibited, leaving conservative participants to gleefully denounce left-wing intolerance.

The police intervention drew a sharp rebuke from the Belgian prime minister, Alexander De Croo, a center-right opponent of the Socialist Party. In a post on social media, he said that Belgium’s constitution guaranteed freedom of speech and that “banning political meetings is unconstitutional. Full stop.” What happened at the conference venue, he added, “is unacceptable.”

Mr. Orban of Hungary, who has been trying to position himself as the leader of a Pan-European movement against what he calls the “woke Goliath,” did not appear to have been in the hall when the police arrived. But he posted a message on the social media platform X comparing the failed intervention to actions by Hungary’s communist authorities in 1988, when security forces tried in vain to silence dissident voices before the collapse of communism.

“We didn’t give up then and we will not give this time either!” Mr. Orban wrote on X.

Hungarian media outlets controlled by Mr. Orban’s governing Fidesz party seized on the ruckus in Brussels as evidence of the Hungarian leader’s importance as a threat to the European establishment. “All of Brussels is working to silence Viktor Orban,” claimed a headline in Magyar Nemzet, an online news site and propaganda bullhorn.

The Brussels event was the latest in a series of conservative conferences, including one held in Brussels two years ago without incident, that have been organized by the Edmund Burke Foundation, a group whose declared goal is “strengthening the principles of national conservatism.”

Yoram Hazeny, the Israeli-American chairman of the foundation, said in Brussels on Tuesday that police officers sent to shut down the event “got scared” when they were surrounded by televisions as they entered the building, and they left. He said he had been told by the police that the two-day conference would be “closed down gradually,” and urged attendees not to leave the building because they would not be allowed back in.

The conference was initially to be held at Concert Noble, a grand former ballroom and high-end events space. But it lost that booking after protests by left-wing activists and relocated to a luxury hotel. When the hotel, under pressure from another Brussels mayor, also canceled, it settled on Claridge, an events space and nightclub near the headquarters of the European Union.

Mr. Kir, the mayor of the Brussels district of Saint-Josse-ten-Noode that includes Claridge, gave no explanation for why he thought it necessary to prohibit the conference from taking place, other than to say that he wanted to “guarantee public safety.” The authorities appeared to have been worried that radical left-wing activists might clash with the conservative participants.

A group called the Anti-Fascist Coordination of Belgium had vowed to disrupt the gathering, saying that “hate speech is never justified by freedom of speech.” It called for a protest late on Tuesday near the conservative conference.

Many of the speakers scheduled to attend the gathering were mainstream hard-right politicians, like Poland’s former prime minister Mateusz Morawiecki, who left office after his right-wing Law and Justice Party lost its parliamentary majority in an October general election.

But they also included Éric Zemmour, a far-right candidate in France’s 2022 presidential election who has been convicted of inciting racial hatred, after saying on television in 2020 that unaccompanied child migrants were “thieves,” “rapists” and “murders.” Organizers said that the police guarding the venue had prevented Mr. Zemmour from entering.

Speaking after the brief police intervention, Suella Braverman, Britain’s former Home Secretary and the darling of hard-right opponents of immigration in the governing Conservative Party, said: “If only the globalists in Brussels put as much energy into securing our borders as they did in trying to gag conservatives, maybe our continent would be in a healthier state.”