At about 1 a.m., a neighbor reported a fire at a single-family Eichler-style home in the 700 block of Duncardine Way, said Capt. Jeff Plecque, of the Sunnyvale Public Safety Department.
Firefighters arrived to find the home engulfed in flames, Plecque said.
There was concern that the residents were inside the home, because there were two cars parked in the driveway, a sedan and an SUV, Plecque said.
Firefighters planned to go into rescue mode, but found it was impractical due to the dangerous conditions and the unlikelihood that anyone trapped inside would still be alive, Plecque said.
He said firefighters switched to a defensive mode and fought the fire from the outside.
Several nearby homes were threatened by the blaze, but were not damaged.
The two-alarm fire was controlled by 2:30 a.m.
No injuries were reported.
The cause of the fire is under investigation. Plecque said firefighting efforts were hampered by a live electrical wire in the backyard, which he said may or may not have caused the fire.
A damage estimate was not immediately available.
The family of four, including two children, who lived at the home, is on vacation in China, Battalion Chief Vince Chetcuti said. Their home was destroyed, he said.
They were informed about the fire this morning.
"They were surprised, but happy at the same time that no one was injured," Chetcuti said.
The cars in the driveway were not damaged.
The Mountain View, Santa Clara, and San Jose fire departments assisted.