A supporter of Brazil’s far-right president, Jair Bolsonaro, has desecrated a beachside memorial to Covid-19 victims as the country’s coronavirus death toll rose above 40,000.

Activists from civil society group Rio de Paz dug 100 symbolic shallow graves on Copacabana beach before dawn on Thursday to represent the Brazilian lives lost.

At least 40,276 people have now died, according to a coalition of news outlets which has been compiling an independent tally since Brazil’s health ministry was accused of seeking to conceal the full figures last week.

Activists dig 100 mock graves on Copacabana beach in Rio de Janeiro, Brazil, on 11 June 2020. Photograph: Carl de Souza/AFP/Getty Images

But the NGO’s founder, Antônio Carlos Costa, said Bolsonaristas began haranging activists as they stood beside the mock cemetery.

Soon after a man was filmed knocking down the wooden crosses protesters had placed in the sand near a banner reading: “Brazil, land of graves”.

“They feel such rage – and I think they’re reproducing the behaviour of the person occupying the highest position in the land,” Costa said of his group’s assailants.

Among those watching the vandalism was a grieving father who campaigners said had lost his 25-year-old son to Covid-19. The man re-erected the crosses and shouted: “Respect the pain of others.”

Costa said he felt anger at the profoundly disrespectful act – the first such attack he had experienced in 13 years protesting against politicians from across the political spectrum.

But he said that most of all he felt pity for the man, and other hardcore Bolsonaristas, who were “so blinded by ideological passion that they had closed their eyes to reality”.

A man knocks over one of 100 crosses. Photograph: Carl de Souza/AFP/Getty Images

Polls show millions have turned on Bolsonaro over his internationally condemned handling of coronavirus, which he has dismissed as “a little flu”. But the rightwing populist maintains a solid support base of about 30%.

“Bolsonaro’s mistakes are not so subtle that only the most perceptive people are able to detect them. It’s all so clear,” said Costa, a Presbyterian church leader. “So how is it that some people cannot see this?”

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Costa said Brazil was experiencing “the worst crisis in its history”.

Related: ‘Enormous disparities’: coronavirus death rates expose Brazil’s deep racial inequalities

“Thousands have died. Families are in mourning. People are unemployed. At a moment like this you might expect the president of the republic to offer words of hope, to show compassion, to behave soberly and signal a way forwards. Instead, we see him joining anti-democratic protests, telling journalists to shut up, riding horses, driving jet-skis [and] organizing barbecues.”

As he smashed the symbolic cemetery, the Bolsonarista branded activists leftist terrorists.

Costa said the memorial had nothing to do with left or right. “What moves us is a commitment to life. They use this discourse to delegitimize anti-Bolsonaro protesters – as if only those on the left were capable of noticing this government’s insane and anti-democratic acts.”