Twenty firefighters from four stations were called to a fire in Cambridge’s south end early Wednesday morning.

Nobody was home around 4:30 a.m., when the fire broke out at a home on State Street, near Ainslie and Water streets.

The building was engulfed in fire when crews arrived, said Cambridge Fire Department captain Mark Yantha.

“The flames were visible from the rear of the building,” he said.

Phil Grosvenor, who lives across the street, said he awakened to the sound of sirens and then noticed an “orange glow” from his neighbour’s ack patio.

“At some points, the smoke was so bad you couldn’t see across the street. It was coming out of the roof and out of the windows,” he said.

Early estimates suggest the fire did $350,000 worth of damage, primarily in the rear of the building.

“The home may have to come down, but that’s going to be up to the insurance and the building department,” said Yantha.

The investigation into what sparked the flames continues.