Officials said a driver of a white SUV struck a fire hydrant and power pole in the 12000 block of Magnolia Boulevard near Laurel Canyon Boulevard about 8:30 p.m.
A woman who lived in a nearby residence rushed out to help the driver was shocked by water energized by the power line and later died.
A husband and wife passing by in a vehicle stopped to help. That woman also was electrocuted.
The driver, identified only as a middle-aged man, suffered minor injuries.
Five others were injured and taken to the hospital. All were Good Samaritans attempting to help the driver.
"The most tragic of situations," said LAPD Capt. Peter Whittingham. "Two of those heroes succumbed to their injuries after having been [shocked] by the downed power line."
"This is one of those cases where the village came to help and the villagers suffered as a result of their good will," he added.
Investigators said excessive speed was likely a factor of the crash. Alcohol was not believed to be involved.
Magnolia Boulevard was closed off from Laurel Canyon Boulevard to Radford Avenue while crews worked at the scene.