A New York visitor is recovering after being punched in the face on an Upper West Side sidewalk Wednesday morning, according to a law enforcement source with direct knowledge of the incident.

The attack happened on West 86th Street, between Columbus Ave. and Amsterdam Ave., just before 10:30 a.m., the FDNY said. Surveillance video shows a group of men walking and talking on the sidewalk when a man dressed in a gray t-shirt and shorts runs behind them, appearing to hold a knife in his left hand.

“It was completely random. The guy came up behind him and hit him,” said an unidentified neighbor. “After he hit this man, he almost completely cut off his ear.”

The 55-year-old victim was recovering in hospital after suffering cuts to his face, cheek and ear, a source told NBC New York. Some good Samaritans at the entrance of a building intervened to help the victim, as they sought to stop the bleeding.

“He was sitting in the doorway. One of his friends took off his shirt and held him against his head,” the neighbor said. “One of the eyewitnesses pointed to a guy who had just taken off around the corner.”

It is not known exactly what led to this attack. Just seconds after the man was seen on video running with a knife, the same man was seen running in the opposite direction while looking over his shoulder.

Police were searching for the attacker and canvassing the area for hours hoping to find additional surveillance video. No arrests have yet been made. An investigation into the incident was underway.