More than 100 Occupy protesters have been arrested in the US city of Oakland after trying to enter the City Hall and a convention centre. Police fired tear gas and smoke grenades to disperse crowds who threw rocks, bottles and other objects. The Californian port city was the scene of similar clashes last October. In December, protesters occupied the port. Oakland is one of several US cities to see mass protests over economic inequality and corporate greed. The movement began with Occupy Wall Street in New York last year and has since spread.