Neighbors reported seeing flames inside a home at 642 N. 13th St. at about 6:15 a.m., San Jose fire Capt. Steve Foreman said.
Firefighters responded and were able to quickly contain the fire by 6:45 a.m., but had not fully extinguished the blaze as of 7:25 a.m., Foreman said.
No one was injured in the fire, but an adult and two children were displaced from the home, he said. The residents are being assisted by the American Red Cross.
The fire initially encroached on nearby power lines, but the lines did not drop to the ground, Foreman said.
The blaze has caused extensive damage throughout the home, but fire officials have not yet made a damage estimate, according to Foreman.
"The whole house is pretty burned up," he said. "It's not livable."
The cause of the fire remains under investigation, Foreman said.