The Fresno Fire Department said the blaze broke out around 5 a.m. Monday morning inside an industrial building at Olive and Fresno near the railroad tracks.
Pope Towing rents the building but when firefighters arrived, five people emerged from the building. The building's owner said he was unaware people were living in his building.
One person was treated for smoke inhalation. The fire also stopped trains from running on a nearby railroad track.
"When we got here we noticed the fire had already breached the sides of the buildings and were impeding on the railroad tracks," said Fresno Fire Battalion Chief Ted Semonious.
Fresno Fire says the building was a total loss. Firefighters still don't know the cause of the fire, but say it started inside the building and then spread to a pickup truck parked outside. At least one other car was parked inside and was also destroyed.