Shocking television pictures showed at least two stricken fans being kicked and stamped on by an angry mob of rival supporters during the match between Atletico Paranaense and relegation-threatened Vasco da Gama.
A helicopter landed on the pitch and ferried one fan to hospital as riot police entered the ground and fired tear gas to bring the situation under control.
There were no police inside the stadium at kick off as a private security company was being used and pictures showed that the rival fans were not segregated.
At one point in the trouble, television pictures showed a group of around 20 Paranaense fans mercilessly kicking a man who was stricken on the ground.
A Paranaense fan was attacked in a similar fashion by Vasco supporters, with one stamping on his neck and then head even though he appeared to be already unconscious.
"For a country that is hosting the World Cup next year this is very sad," Vasco da Gama goalkeeper Alessandro told Brazilian television. "The stadium isn't safe."
"We're a bit worried," he added, shortly before the match resumed.
The game was held in the small Arena Joinville because Paranaense's ground is being modernised to host four matches in next year's World Cup.
Brazilian media said that three people were detained in hospital in a serious, but not life-threatening, condition.