The National Guard has been deployed in the US state of Wisconsin after rioting erupted in the wake of a police shooting of an armed suspect.

Officials in Milwaukee said police body cam footage showed 23-year-old Sylville K Smith running towards the officer with a gun in his hand, and said he refused orders to drop it before he was shot.

Violence broke out in the notorious Sherman Park neighbourhood of the city on Saturday night into Sunday, with businesses and cars set alight and gunshots fired by demonstrators angry at the killing.

Milwaukee Police Chief Edward Flynn said 17 people had been arrested, while four police officers were treated for injuries and released.

Wisconsin Governor Scott Walker activated the National Guard as back-up for police should trouble begin to boil over again.