Rowdy fans trying to enter a concert by the Rolling Stones without having tickets fought running battles with police Thursday and authorities said at least 20 people were injured.

Dozens of the fans were detained, police reported.

The clashes broke out when scores of fans were stopped by police at the entrances to the Monumental soccer stadium where Mick Jagger and his band were to perform later.

Police fired rubber bullets and used water cannons and clubs. The fans replied by throwing rocks and bottles at police.

Local television showed the fans being chased by police in the streets.

The Emergency Medical Service reported that at least 20 people were injured, including a television cameraman with a bleeding head.

Police had reinforced security at the stadium after minor incidents had already occurred at the Stones' first concert here Tuesday. More than 50,000 people wearing Stones T-shirts and wagging-tongue tattoos attended that concert. A similar crowd was expected Thursday night