Riot police firing tear gas and brandishing batons clashed Tuesday with bands of youths who shattered windows and looted shops at a major Paris train station. Officials said nine people were arrested. Officers and police dogs charged at groups of marauding youths, some of them wearing hoods, who mingled with commuters and travelers at the Gare du Nord - one of Paris' most important transport hubs. Youths threw trash cans and other objects at officers and set fire to an information booth inside the station. Transport officials said the violence started with an altercation during a ticket check, but youths disputed that account.