Activists angry at Brazil's response to Covid-19 have created 100 graves on Rio's Copacabana beach to remember the more than 40,000 people who have died.
However, organisers said supporters of President Jair Bolsonaro mocked the event with one man pulling out crosses.
The president's opposition to lockdowns and his downplaying of the virus have deeply divided the nation.
Brazil has the world's second-highest number of cases – and the third-highest number of deaths in the world.
On Thursday, deaths passed 40,000 and cases rose to above 800,000, according to the health ministry.
The symbolic graves, with black crosses, were dug before dawn opposite the Copacabana Hotel by members of the Rio de Paz group.
Organiser Antonio Carlos Costa told Reuters news agency: "The president has not realised that this is one of the most dramatic crises in Brazil's history.
"Families are mourning thousands of dead, and there is unemployment and hunger."
But he said some supporters of the president had mocked the project.
"They feel such rage – and I think they're reproducing the behaviour of the person occupying the highest position in the land," he said.
One man went around knocking down the crosses.