The fire was reported at about 8:40 a.m. at a double-wide mobile home located at 1150 W. Winton Ave., Hayward fire Capt. Thor Poulsen said.
Firefighters saw smoke coming from the back of the structure and were able to extinguish the fire, which had also spread to the attic of the mobile home, Poulsen said. No residents or firefighters were injured, he said.
The mobile home was empty at the time of the blaze, but its owners arrived at the scene afterward and said there were three small dogs inside. Firefighters went into the home and found the Chihuahuas dead inside, according to Poulsen.
Hayward's animal services bureau was called to the scene to handle the animals, he said.
The mobile home was completely destroyed in the fire, Poulsen said.
He said investigators were at the mobile home as of 10 a.m. today to try to determine the cause of the blaze.