The shooting was reported at about 10:30 a.m. today at a home in the 4100 block of Laguna Avenue.
Oakland police spokeswoman Johnna Watson said investigators believe the incident was a home invasion robbery because the suspect forced entry into the woman's residence.
Watson said a preliminary investigation indicates that the suspect fired a single shot that struck the woman, and then he fled the scene. It's not clear if the suspect took anything before he fled, she said.
Watson described the suspect, who is still at large, as a black man in his 20s who is about 6 feet tall and weighs about 175 pounds. The man was wearing all-dark clothing and was armed with a gun, she said.
"Historically, this neighborhood has been very quiet and a close-knit community, and this is the first home invasion robbery that's been reported here in a long time," Watson said.
Garrick Chinn, 68, said he was at his mother's home next door to the victim's house when he heard what he said sounded like a phone book hitting the front door of his mother's home.
Chinn said he then heard a car speeding away and police arrived a few minutes later.
He then saw the 81-year-old woman being carried away on a stretcher to a waiting ambulance, but he said she appeared to be "responsive."
Chinn said police officers told him that the bullet had passed through the victim and gone through the side of her house, finally hitting the outside of his mother's house, where it fell onto the concrete.
"I feel fortunate that this didn't happen at my mother's house," Chinn said.
He said he doesn't know the victim well, but said she appeared to be in good health prior to today's incident, although he said her husband died in the past year.
Chinn said home invasion robberies are "unusual" in the neighborhood but noted that his mother's home was broken into several years ago.
He said the shooting today "shakes my confidence in the neighborhood."
Buzz Brown, 53, who lives two blocks away, said there are "daily break-ins of cars" and other crimes in the neighborhood.
Brown said he believes the homes in that area "are easy targets" because Oakland doesn't have enough police officers to patrol the neighborhood regularly.
Brown said officers did a good job of responding quickly to the incident today but added, "they're not here all the time."