Hundreds of protesters gathered after the shooting, with riot police pushing them back with shields and batons
Protests erupted overnight in Philadelphia after police shot dead a 27-year-old Black man holding a knife in the latest police killing to spark anger in the United States, just a week before the election.
Local media reported that two officers shot the man on Monday afternoon after he refused to drop the knife as his mother tried to restrain him, though his family questioned why lethal force was needed.
Hundreds of protesters gathered after the shooting, with riot police pushing them back with shields and batons.
During a night of sporadic riots and looting in the city, around 30 police officers were injured, including one whose leg was broken when hit by a truck.
The US has seen a wave of protests and rioting since the police killing of George Floyd in May in Minnesota, when an officer was filmed pressing his knee to handcuffed Floyd's neck until he went limp.
Many of the protests have accused the police of racism and brutality, but President Donald Trump has focused on the unrest to bolster his claims to be the "law-and-order" candidate in his election battle against Joe Biden.
US media said a phone video of Monday's killing showed Walter Wallace, who suffered mental health issues, pushed his mother away and then walked toward the police.