RIO DE JANEIRO, Dec. 8 (Xinhua) -- Brazilian prosecutors will this week investigate a riot that left four football fans injured and raised fresh doubts about the country's ability to host next year's World Cup.
The Campeonato Brasileiro match between Atletico Paranaense and Vasco da Gama was stopped for almost an hour when rival fans clashed at Arena Joinville in Brazil's southern state of Santa Catarina.
"I saw everything. We will be filing a report," said Paulo Schmitt, prosecutor of Brazil's superior sports justice tribunal (STDJ).
The injured fans are Estevao Viana, William Batista, Gabriel Ferreira Bitael and Diogo Cordeiro da Costa, according to sports news portal Uol.
There were unconfirmed reports that at least one of the injured was in a coma.
The match was played at a neutral venue due to a history of violence between supporters of the clubs.
Police were not initially at the venue due to a local law preventing police from providing security at "private" sports events, local media said.
The brawl broke out 10 minutes after kickoff when a group of supporters breached a security barrier separating the rival fans.
As the tumult escalated, players from both sides gestured to the stands in an effort to calm their respective fans.
Order was eventually restored when guards from a private security firm fired rubber bullets.
Players and officials were visibly shaken by the incident, with some reduced to tears and declining television interviews.
"It's sad to see images like this when the country is preparing for a World Cup," Vasco da Gama coach Adilson Batista said.
Atletico Paranaense coach Vagner Mancini said: "I just want to leave and go home. I have never seen anything like it."
Prosecutors last month called for a national debate to curb rising violence among Brazil's notorious supporter groups.
In one episode in October, four fans of Serie B club America were shot after a match against Ceara near the World Cup host city of Natal.
In February a teenager died when hit by a flare launched by a fan of Brazilian club Corinthians during a Copa Libertadores match.