Police responded to reports of a shooting at 1:35 a.m. at a taco truck parked near the corner of Fruitvale Avenue and Foothill Boulevard, Officer Johnna Watson said.
Watson said the truck's owner was outside sweeping and doing other maintenance work when an armed man approached him and demanded money.
The truck owner was carrying a gun as well, and the two exchanged fire.
Both were shot, and were taken to hospitals, where they are in stable condition today.
The suspected robber has been placed under arrest but remains in the hospital under guard, Watson said.
Police have also detained two other people believed to be connected to the robbery, an adult man and a juvenile.
Officers canvassed the neighborhood this morning looking for witnesses and are trying to obtain surveillance video footage from nearby businesses.
This morning's incident is the latest in a string of robberies of taco trucks, Watson said. She said the trucks are inviting targets for robbers because they stay open late and deal in cash.
Oakland police have increased patrols in areas with late-night taco trucks, Watson said.
A shooting at an Oakland taco truck on Dec. 30 killed 5-year-old Gabriel Martinez, Jr. The boy was at the truck in the 5400 block of International Boulevard with his father, who owns the truck, when a gunman opened fire at about 8:40 p.m.
Police are still investigating that shooting, but have said they don't believe the boy was the intended target.