It was meant to be a celebration to mark the 25th anniversary of the Velvet Revolution, the peaceful uprising against Czechoslovakia’s communist regime in 1989. Instead, events in Prague on Monday felt more like an uprising against the current president of the Czech Republic.

Milos Zeman was pelted with objects including eggs, sandwiches and tomatoes as he stood alongside with the presidents of Germany, Hungary, Poland and Slovakia at the university campus where a student rally launched the revolution in Czechoslovakia a quarter century ago.

Security guards used black umbrellas to shield Zeman and other presidents from thrown objects. According to the German embassy in Prague, the German president, Joachim Gauck, was hit in the head by an egg as the presidents were unveiling a plaque to commemorate the 1989 events. In a speech, Gauck had praised “all the people who aren’t satisfied with their powerlessness, and who break out of their powerlessness to creative shape their freedom”.

The crowd repeatedly shouted “Shame, shame” and “Resign, resign”, at Zeman, while the other presidents were applauded. At 11.10am, in a pre-agreed moment, thousands of protesters brandished red cards at their president, while others carried banners saying: “We don’t want to be a Russian colony.”

“I’m not afraid of you!” Zeman retorted to the crowd, while security guards shielded him. “Twenty-five years ago it was dangerous to go out on the streets. It required courage. I was among the demonstrators then. It is cowardly of you to come here and pelt us with eggs.” Zeman’s supporters were due to hold their own rally on Monday night.

Anger in the Czech Republic has been growing against Zeman as critics accuse him of betraying the commitment to human rights enshrined by Václav Havel, the hero of the Velvet Revolution who became Czechoslovakia’s first post-communist president. A giant picture of Havel was hanging above the protesters on Wenceslas Square, adorned with the slogan “Havel forever”.

Zeman’s opponents referred to his pro-Russian stance in the Ukraine conflict, recent praise of Chinese leaders on a visit to China and comments seen as downplaying the police crackdown 25 years ago.

He also used attracted criticism by using expletives when explaining in a live radio broadcast why he did not consider the Russian punk group Pussy Riotpolitical prisoners. Some of its members spent time in a Russian prison camp on hooliganism charges.

The centre of Monday’s commemoration was the street in downtown Prague where police brutally attacked a peaceful anti-communist student march that came a week after the collapse of the Berlin Wall on 17 November 1989.

The Velvet Revolution began with fiery speeches against the hardline communist regime at Charles University, prompting thousands of students to march through Prague. The police blocked the street from both sides, squeezing the path of protesters with armed vehicles before attacking them with truncheons; hundreds were injured. Undeterred, the students continued to protest and crowds grew in the days that followed with a general strike held on 24 November.

On 29 December 1989, Havel, a dissident playwright, became president. Democratic elections took place a year later.

• This article was amended on 18 November 2014. The original said that in 1989 Havel became Czechoslovakia’s first democratically elected president since 1946. In fact, Havel was made president by assembly in December 1989. The first democratic elections didn’t take place until June 1990.