Residents of a home in the 2000 block of Commodore Drive, near Penitencia Creek County Park, called 911 at 8:38 a.m. to report a fire at the residence, San Jose fire Battalion Chief Jose Guerrero said.
Fire crews arriving on the scene saw heavy fire coming from the back of the home and flames that appeared to be shooting through the roof, Guerrero said.
After learning that a grandmother in her 70s was trapped inside, firefighters entered the burning home to rescue her.
"They were on their hands and knees throughout the house searching" as heavy pieces of the home's red-tiled roof fell to the ground, the battalion chief said.
Firefighters were able to locate the woman in a back bedroom and pulled her outside. She was taken to a hospital in critical condition, Guerrero said.
A man living at the home was taken to a hospital to be treated for smoke inhalation and another resident was uninjured.
Firefighters were eventually able to contain the fire, which gutted the inside of the home and caused about a quarter of its roof to collapse, Guerrero said.
The fire began in the home's kitchen and dining area and spread to a back patio and through the roof, he said.
Guerrero said the cause of the fire was apparently not cooking-related but has not yet been determined.
The battalion chief said he did not know whether the home had working smoke detectors.
"If you have a working smoke detector, it will alert you to the fire when it's still small and it will not get to this condition," he said.