The fire that first started in a large field was reported just before 1 p.m. near McVay and Fleming avenues.
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The firefighter was treated for dehydration at the scene and released.
One person was displaced by the blaze.
"Right now, the heat is taking its toll on firefighters that are fighting this fire. The civilians that are in this area should stay out of the sun, stay plenty hydrated and avoid activities that are going to cause more fires," said Capt. Mitch Matlow.
According to the San Jose Fire Department, the blaze was sparked by a downed power line and spread up a hill where it quickly engulfed a home.
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Firefighters said two homes caught fire. One of the homes was next to Raymond Su who lives next door and called 911.
"I was on my deck working and looking over the valley, and then I heard some popping noises, and I thought that's not good," said Su.
"After a little while, like 15-30 seconds or so, I saw flames start, and that's when I called it in," he said.
Many in the neighborhood couldn't get back into their homes right away.
Tuesday's fire comes as high temperatures continue across the region. Though a Spare the Air Alert is in effect, a Red Flag Alert has not been called.