Protesters have swarmed the streets of West Philadelphia, leading to a violent standoff between them and law enforcement after police officers fatally shot a 27-year-old black man armed with a knife during a confrontation on Monday afternoon.

Protesters and police clashed outside the local police district headquarters in the wake of the shooting with reports of looting and police vehicles being set on fire in the neighborhood.

'Put the Knife Down'

Walter Wallace Jr. shooting
A still from the cellphone video shot by the bystander. Twitter

Shortly before 4 p.m. on Monday, police officers responded to reports of a man armed with a knife. The man was identified as Walter Wallace Jr.

Video footage shot by a bystander showed two Philadelphia police officers with their guns drawn at Wallace, who is carrying a knife in his right arm. Wallace's mother can be seen desperately trying to stop him as the officers are heard saying "put the knife down."

Wallace walks around some vehicles parked on the street and continues to approach the officers as they back away from him with their guns drawn. The camera briefly points downward as Wallace advances towards the officers but appears to be several feet away from them when they fire multiple shots at the man before he collapses on the street.

Wallace's mother can then be seen screaming and running up to him. "Oh my god! They just killed him in front of me," the bystander filming the video can be heard saying before several bystanders gather around Wallace, who is then rushed to the Penn Presbyterian Medical Center, where he was later pronounced dead.

Officers Under Investigation

The officers involved have been taken off street duty pending an investigation, according to Philadelphia Police Commissioner Danielle Outlaw.

"I have directed the Officer Involved Shooting Investigation Unit to begin its investigation. I recognize that the video of the incident raises many questions. Residents have my assurance that those questions will be fully addressed by the investigation," Outlaw said.

"While at the scene this evening, I heard and felt the anger of the community. Everyone involved will forever be impacted. I will be leaning on what the investigation gleans to answer the many unanswered questions that exist," she added.

Philadelphia Mayor Jim Kenney also released a statement over the shooting. "My prayers are with the family and friends of Walter Wallace," Kenney said. "I have watched the video of this tragic incident and it presents difficult questions that must be answered."

Philadelphia Up in Flames

Videos being circulated on social media show scenes of violence and unrest in West Philadelphia, including footage of police using riot shields to push back protesters as they hurl projectiles at them outside a police precinct, a police SUV set ablaze by protests, and looting.