The incident happened just before noon.
According to Metro, the man got off the Bus Line 16 near West 3rd Street and Lucas Avenue when he was shot.
The victim and two suspects had gotten into some sort of confrontation near the intersection, the Los Angeles Police Department said.
"Following the incident, he re-entered the same bus seeking refuge," the statement from Metro read. "Metro thanks the bus operator for his quick response in allowing him on the bus and transporting the individual to a nearby hospital. Unfortunately, the victim succumbed to his injuries."
Meantime, the suspects remain at large.
Anyone with information is being asked to call the L.A. Regional Crime Stoppers Hotline at 800-222-TIPS or (800)-222-8477.