OAKLAND, Calif. (AP) - A crowd of protesters in Oakland, Calif. that had gathered in front of City Hall amid a heavy police presence scattered Tuesday night after authorities fired tear gas in response to rock throwing from some of the demonstrators.

The police action was the second such incident in as many hours. Officers in riot gear briefly dispersed a crowd heading back toward the downtown area where an Occupy Wall Street encampment was dismantled earlier in the day.

Authorities denied reports that they used flash bang canisters to help break up the crowd, saying the loud noises came from large firecrackers thrown at police by protesters.

The skirmishes come after police removed about 170 demonstrators who had been staying overnight on a plaza outside City Hall for more than two weeks. City officials say 85 people were arrested in the morning raid.