Dozens of fans fought a savage battle on the terraces at a Brazilian championship match on Sunday, interrupting play for more than one hour and leaving at least three people reportedly hospitalised in serious condition.
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. The trouble occurred even though the stadium was half-empty.
"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.
Paranaense, winning 1-0 at the time, went on to win 5-1, condemning former South American champions Vasco to relegation. Paranaense finished third to qualify for next year's Libertadores Cup.
The incidents completely overshadowed the rest of the final day of the Brazilian championship during which Vasco's Rio de Janeiro neighbours Fluminense were also relegated.
Fluminense became the first defending champions to be relegated the following season, despite a 2-1 win over Bahia in their final game.
Image: Vasco da Gama soccer fans beat up an Atletico Paranaense fan
Photograph: Carlos Moraes/Agencia O Dia/Reuters