Crews were called to the building near the intersection of Sacramento and Locust streets around 2:30 p.m. Saturday.
Smoke and flames billowed from the buildings at the height of the fire. Witnesses say they heard popping coming from the alleyway between the buildings before the fire started.
Officials aren't sure yet how the fire started, but it did damage two businesses -- Luna Boutique and Dolce & Salato
"I was just concerned cause I saw people coming out of the buildings and people were just shell-shocked, they were so scared," witness Jaime Webber said. "So I was a little nervous. And it looked like it was traveling quickly, so that's why I was nervous. Orange flames were coming out of the roof. And as firefighters exposed more of the roof, more orange flames were coming out of the top."
It took less than an hour to knock out the fire. A large crane was brought in to fight the blaze from above as well as the ground.
There are at least six apartments in both of the buildings. At least a couple of residents were inside the building when the fire broke out. The American Red Cross was called to provide temporary housing assistance for up to four people.
Some people reported seeing flames as far away as Marin County, which is a testament to how big the fire actually was.
PG&E was also on the scene as of 3:20 p.m. responding to reports of a smell of gas near the building.
No injuries were reported. The cause of the fire is under investigation.
(Bay City News contributed to this report)