Police said two officers were injured Saturday and three people were arrested at a protest rally near a summit of Pacific Rim leaders.
Police did not provide any details of the circumstances in which the injuries occurred. A police spokeswoman, who gave the information on customary condition of anonymity, said one of the officers was being treated for a head injury.
There were no signs of widespread violence at Saturday's protest, in which about 3,000 people marched along a heavily fortified route from Sydney's Town Hall to nearby Hyde Park, several blocks from the summit site.
Protesters had a hodgepodge of issues, from the Iraq war to gay right and global warming.