Firefighters responded to a single-family home on East 12th Street at about 2:50 a.m. Crews saw heavy smoke coming from the home when they arrived.
Three residents were transported to an area hospital to be evaluated after they suffered smoke inhalation while they were escaping.
One person was then transferred to UC Davis Medical Center's burn unit for minor burns and severe smoke inhalation, fire officials said.
A passerby, who noticed smoke coming from the home and heard pleas coming from inside, helped the people escape.
The fire originated in the kitchen, but the exact cause hasn't been determined. The home didn't have smoke alarms.
The estimated damage to the property is $70,000, fire protection district officials said.