The chief said that were it not for officers immediately transporting the child to the hospital in their cruiser, medical staff said he would not have survived.
The child remains in critical but stable condition after severe damage to his torso, police said.
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The boy was shot shortly after 8:30 p.m. in the 2500 block of 26th Avenue in East Oakland.
Police have opened an investigation, but the chief said that it is "possible" that a relative was involved in the shooting. He said that investigators are looking at the ownership of the firearm that was used and seeing if that matches any of the relatives that were in the vehicle at the time.
"I don't believe that a family member intentionally fired a gun and injured that child," said Chief Armstrong, adding that it would be good for the person to come forward, saying it would be the "compassionate" thing to do, considering the suffering that the child is undergoing.
Anyone with information about the shooting is asked to please call the Oakland police felony assault unit at (510) 238-3426.