Authorities responded to the robbery call at the business in the 1200 block of East Anaheim Street in an area known as Cambodia Town at 11:48 a.m. Police say a gunman walked in and confronted the owner.
The victim struggled with the armed suspect, and during the scuffle, the suspect's gun went off. No one was hit, but the owner was injured in the confrontation.
Two bystanders, who were at a restaurant next door, heard the commotion and ran over. The men were in town from Boston for a martial arts convention.
Seiha Hak said he chased after some of the suspects, but they fled in a car. Then he heard a woman screaming that another suspect was still inside the store.
"So I took him down ... and then my master right here came in and kicked the gun away," he said.
The business owner and the suspect were taken to a local hospital for non-life threatening injuries. Long Beach police say it is not yet clear if there were any outstanding suspects.
Anyone with information about the incident is urged to call the Long Beach Police Department at (562) 570-7464.
Correction: An earlier version of this story incorrectly spelled Seiha Hak's first name. We apologize for the error.