A 21-year-old was killed by a shot to the head during a confrontation that involved almost 500 fans before a match between Brazilian rivals Corinthians and Palmeiras yesterday afternoon.

Three other people were seriously injured, including one that required surgery after being shot in the hip.

Witnesses have reported seeing a group of Palmeiras being ambushed by Corinthians supporters in the city's north side.

Four people have been arrested so far, although it is unclear if any of them was involved in the shooting.

Reports have suggested that the fight was arranged on a social networking site.