The incident, captured on cell phone video, happened in the late afternoon on Tuesday at the corner of East 149th Street and Third Avenue in the Melrose section.
Thursday night, the NYPD released the pictures of two suspects wanted in the attack.
William Burgess, 21
Enrique Foote, 18
As seen in the video, five suspects approached 53-year-old Souleymane Porgo, a father of two, at his purse stand and began punching him repeatedly before leaving him on the ground unconscious.
"In the beginning, he got knocked down to the floor, the victim, and then he got right back up," said the witness who took the video. "And that's when the dude in the red sweater knocked him out in one punch, and that's when everyone else gave him like two haymakers right there, and he didn't move after that."
The attack unfolded after an incident earlier in the day, during which police say one of the suspects allegedly tried to steal a purse.
"Honestly, that's pathetic if you ask me," the witness said. "I don't see the point of starting so much violence over a little purse, if that's what happened of course."
Police say the attempted thief left and later returned with four other men to beat up the vendor.
"I don't know if he was offended by something he said, but he started screaming, 'I'm from around here, I'm from around here,'" the witness said, "And then, like a couple seconds later, I just heard him yell, 'Right now, right now!' And then that's when he ran across the street and came back with about four or five of his buddies right there."
Porgo is currently at Lincoln Hospital in critical condition with a fractured skull and bleeding in the brain.
"Honestly, everybody was so terrified they didn't even dare to get close to that group after they started beating the guy up," the witness said. "But as soon as they were gone, everybody ran and started helping the guy."
All five suspects are believed to be in their 20s.
The first was last seen wearing a red baseball cap, a red hooded sweater and blue jeans.
The second suspect had glasses and was wearing a black baseball cap, a black T-shirt and black jeans.
The third suspect wearing a white T-shirt, blue shorts and black sneakers.
The fourth suspect had glasses and was wearing a gray T-shirt and red pants.
The fifth suspect was wearing a pink baseball cap, a pink sweater and black jeans.
Anyone with information is asked to call the NYPD's Crime Stoppers Hotline at 1-800-577-8477, submit tips online at NYPDCrimeStoppers.com, or text any tips to 274637 (CRIMES) and then enter TIP577.