Police fired rubber bullets and tear gas as rioters pelted them with rocks. The fighting at Buenos Aires' Constitucion station spilled into a nearby street as demonstrators shattered windows, set fire to a ticket sales area, looted shops and ripped pay phones from walls.

Hundreds of passengers fled the fighting inside train station, one of the largest in South America with an estimated 300,000 users daily.

Twelve police officers were injured by flying rocks, mostly with cuts and bruises to the head and chest, and nine people were also treated at the scene for smoke inhalation, said Alberto Crescenti, a spokesman for emergency medical workers.

Police Commissioner Ricardo Falana reported 16 arrests, including two minors.

He said about 100 police were needed to quell the rioters, who he said threw a "hail of rocks" at officers. Firefighters quickly put out small fires in trash cans and the ticket area. Fernando Jantus, a spokesman for the Metropolitano train concession, said service was interrupted at the evening rush hour because a train broke down on a track just outside the station, blocking other trains from leaving the station.

Passengers have long complained about poor commuter rail service on lines leading from Constitucion station in downtown Buenos Aires to the capital's poor southern suburbs.

Buenos Aires area commuter rail lines were privatized in the 1990s under then-President Carlos Menem but passengers for years have complained about the failure of new operators to provide timely service on oft-crowded routes.