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As many as 50 people have been evacuated from a Berkeley apartment building that burned for nearly four hours early this morning and four buildings surrounding it, a deputy fire chief said.

Two walls of the building at 2227 Dwight Way were evaluated as unsafe and at risk of collapse by a structural engineer this afternoon, Berkeley Deputy Fire Chief Gil Dong said.

Residents of four adjacent buildings will remain displaced until crews can come in tomorrow to resolve the structural issues, as officials fear that a collapse could damage the surrounding buildings, Dong said. 

The fire at the six-unit building located a few blocks from the University of California at Berkeley campus was reported at 4:13 a.m. 

The roof of the building collapsed, which made it difficult for firefighters to access various hot spots that remained from the blaze, Dong said. The fire was under control at 8:05 a.m., he said. 

All residents were safely evacuated from the building, according to Dong. No injuries to any civilians or firefighters were reported because of the fire, he said. 

Investigators have determined the fire was accidental, but have been unable to determine the exact cause, Dong said. 

The fire began in a closet which housed two water heaters, which contained multiple heat sources including a natural gas appliance, electrical outlets and heating vents for the wire heaters themselves, Dong said. 

"There's nothing there to indicate this fire was intentionally set," he said.