The incident involved the last float of the first samba school parading through Rio's Sambadrome. The float of samba school Paraiso de Tuiuti crashed into a fence that separates the stands from the pavement, injuring spectators, revellers and journalists. One reporter had an exposed fracture.
Police began an investigation as soon as the float finished its transit through the Sambadrome.
Police investigator William Lourenco Bezerra said the three conductors of the float would be questioned on Monday, adding that one driver already had been identified as the main focus of the probe.
"The last float went into reverse and ended up pressing revellers against the fence on one side. That caused chaos. Then the conductors made a quick manoeuvre to the opposite direction and injured more people," Bezerra said.
"The main conductor of the float mixed with the rest of the samba school and left. But he has already been identified and will be investigated."
Rio's state health secretary said in a statement that eight of the 20 people involved in the incident are in hospital and three women were in serious condition.
