The blaze continued to burn at 11 a.m. while crews battled the flames that heavily damaged at least 26 apartments.
The fire on the 400 block of South Mt. Vernon Ave. created traffic problems for motorists trying to navigate the intersection of Mt. Vernon Avenue and Chestnut Street.
The origin of the blaze was under investigation. The fire spread from a first-floor corner unit to the second floor. Many people were asleep when the fire started.
All of the building's 30 units have extensive fire and/or water damage.
The Inland Empire Chapter of the American Red Cross is offering food and shelter to fire victims. The Red Cross set up a shelter at Richardson Middle School, 455 South K St. in San Bernardino.
The Red Cross is helping about 125 people. Eighty people were staying at the Red Cross shelter Sunday night. Many of the residents staying at the center are children.
"First night's always great for them because it's like a big sleepover," said Red Cross worker Robert Bahler. "It hasn't really sunk in. The second and third nights are when it really starts to hit them hard. So we're here, we have mental health counselors on scene to just see how they're doing, see how they're recovery's happening."
The Red Cross will still be able to use Richardson Middle School Monday as the shelter since there is no school on Presidents Day. A different site is being sought so the Red Cross can operate the temporary shelter for the displaced families.