"According to the current information, the officer noticed two men that were beating a person lying on the ground, and interfered. The officer made himself known as a policeman and demanded that the men stopped. As an emergency measure, the officer made a warning shot," the statement of the police said.
The policeman and the injured man then retreated to a kiosk, while the attackers fled the scene.
According to the police, ongoing anti-G20 protests in Hamburg have already resulted in injuries to at least 196 police officers, and a total of 83 protesters were detained.
Security at the summit is being provided by a total of 20,000 policemen from all over the country, and the police have reportedly requested additional support from other German federal states as more protests are expected on Saturday.