The two-story building houses a Peet's Coffee & Tea and the Calla women's boutique on the ground floor, and offices on the second floor, Schapelhouman said.
Firefighters headed to the building, located at University Drive and Santa Cruz Avenue, around 7 a.m. after being notified by American Lock and Alarm that a fire alarm had been activated there.
Arriving crews saw smoke on the second floor and located the fire behind a bathroom in an area that contains electrical panels, Schapelhouman said.
Schapelhouman said the fire had already spread into the walls and the floor and may have started overnight.
"This thing had been burning for a long, long time," he said. "It had a really good head start on us."
Firefighters quickly upgraded the response to a second alarm, then called for a third at 8:03 a.m. and a fourth at 9:20 a.m.
Crews rotated in, working 20-30 minutes at a time, breaking through floors and ceilings and stripping walls in order to locate and extinguish all the fire spots, Schapelhouman said.
The blaze was declared under control at 8:30 a.m. but crews continued to battle hot spots until about 1:30 p.m.
"It was a very stubborn fire," he said. Firefighters were "playing a little game of hide-and-go-seek ... trying to see where it had gone."
One firefighter suffered a shoulder injury and was taken to Kaiser Permanente in Redwood City where he was treated and released.
Some of the worst damage occurred at the Calla boutique, where firefighters broke through the ceiling searching for flames, Schapelhouman said. The shop also sustained extensive water damage.
"It was a lake," Schapelhouman said.
As some firefighters battled the fire, others worked to remove merchandise from the store.
"We tried to do the least amount of damage as possible," Schapelhouman said.
"In this economy we're pretty sensitive to trying to help out the business owners the best that we can so that they can survive this," he said.
He said he believes the building is salvageable but that it will need extensive work to repair the damage.
"The sad part about this fire is that it is going to displace a number of businesses for an extended period of time," he said.
The cause of the fire remains under investigation but Schapelhouman said it may be related to the heating and ventilation system or electrical wiring.
The building was not equipped with a sprinkler system.
The fire response included about 70 firefighters, 14 engines and four trucks from various agencies.