The crash was reported at 11:37 a.m. in the area of 20491 Almaden Road, just outside of San Jose city limits.
Fire crews arrived and found that a green, four-door vehicle had gone off the roadway and was up against a tree, San Jose fire Capt. Steve Foreman said.
The car was severely damaged and the occupant, a woman in her 30s, was trapped inside, Foreman said.
Crews worked for about 45 minutes using tools including the Jaws of Life and were eventually able to extricate the woman, he said. She was taken to a hospital by ambulance with serious injuries.
The California Highway Patrol is investigating what caused the crash, Foreman said.
"It was raining at the time of the accident and the roads were wet," he said.
He said the woman was wearing her seat belt, and her airbag deployed.