Oakland firefighters extinguished the two-alarm fire at Claremont Middle School on College Avenue near the Rockridge BART Station, firefighters had extinguished the fire at about 3:10 a.m., Battalion Chief Geoff Hunter said.
The fire broke out after 1 a.m. on Monday.
The investigators say the fire started in the cafeteria and spread into the attic. Flames were so big, they could be seen from the freeway.
"The building is large building, the fire had a good head start on us, because of the high ceiling and thick acoustic tiles on the ceiling... It makes it very difficult to get to it," said Oakland Fire Department Battalion Chief Geoff Hunter.
According to the battalion chief on scene, crews found signs of forced entry when they arrived. Hunter said crews found an exterior door open at the school, that was forced open. He says that is unusual.
Police said that an arson investigator responded to look into the possibility the fire was intentionally set. Police have no suspects so far, but they did find a fire extinguisher, which suggests the fire may have been an accident.
Meanwhile, School Board Member Jody London was distraught to hear that investigators were looking in to the possibility that someone broke into the school. She surveyed the damage early Monday morning.
"We have a lot of kids who come to this school and rely on the food program for breakfast and lunch, and that is unfair to them," she said.
The school district is yet to decide if school will be open on Tuesday.
"I don't want to alarm people or have them jump to the conclusion that we won't have school because the fire was primarily located in the kitchen and cafeteria area, and there are other ways we could provide lunch and the keep the rest of the school day close to normal," said Troy Flint, a spokesperson for the school district.
If the utilities are undamaged, the school will likely open normally Tuesday and provide brown bag lunches in lieu of hot lunches.
A portable unit equipped with a kitchen could be brought to the school as soon as next Monday and the school could resume serving hot lunches, Flint said.
Here's what the inside of Oakland's Claremont Middle School's cafeteria/kitchen looks like after overnight fire. pic.twitter.com/jBi2JQLTIl— Amy Hollyfield (@amyhollyfield) February 16, 2015
Neither firefighters nor civilians were injured in the blaze.
The school was closed in honor of President's Day.
Bay City News contributed to this story.