The shooting happened at 1:08 p.m. in the 1800 block of West Avenue J, according to Los Angeles County Sheriff's Deputy Raquel Utley.
The man was transported to a hospital, where he was pronounced dead, Utley said. His name was withheld pending notification of next of kin.
A news photographer at the scene told City News Service that the man was standing in a doorway to Tom's Restaurant and refused to drop the knife. Instead, he allegedly pulled out a crossbow-type weapon from his backpack, prompting the shooting.