The graves were dug overnight on the beach opposite the ritzy Copacabana Hotel in a protest mounted by non-governmental organization Rio de Paz.
Brazil has become a major epicenter of the coronavirus pandemic, with 39,680 deaths and over 770,000 confirmed cases as of Wednesday, the world's worst outbreak after the United States.
Far-right President Jair Bolsonaro has downplayed the gravity of the pandemic and pushed local governments to lift quarantine measures, sending contradictory signals to Brazilians on whether to use masks and practise social distancing.
"The president has not realized that this is one of the most dramatic crises in Brazil's history," said organizer Antonio Carlos Costa, who criticized Bolsonaro for not showing solidarity with the suffering.
"Families are mourning thousands of dead, and there is unemployment and hunger," he said.
Not everyone agreed with the protest.
An angry man pulled out crosses, shouting against the symbolic tribute. Another man, who said his 25-year-old son died of COVID-19, went around replacing the fallen crosses.
"It's such a tragedy," said passer-by Marcia Lucia Dias. "It's frightening to see the crosses. But this is really happening. Our authorities contradict themselves and we don't know what to do." (Reporting by Sergio Queiroz and Rodrigo Viga Gaier; Writing by Anthony Boadle; Editing by Rosalba O'Brien)
epaselect epa08479374 Aerial photograph taken with a drone that shows activists as they place one hundred and ten crosses, as a way of denouncing the errors made by the Government in managing the coronavirus crisis, during a protest organized by the NGO Rio de Paz, on Copacabana beach , Rio de Janeiro, Brazil, 11 June 2020. EPA-EFE/ANTONIO LACERDA 