CAMPBELL, Calif. (KGO) -- Police and firefighters battled a fire at a 50,000 square foot vacant building in Campbell on Friday.
On Saturday, Justin Stockman from the Santa Clara County fire department told ABC7 News the fire is contained, but not extinguished. "The sheer size of this building and the amount of burnable material means it will likely smolder for some time," he said.
SKY7 was over the fire at Knowles and Dell Friday, which were closed between Winchester & Division.
Officials tweeted around 11:50 a.m. on Friday the fire was upgraded to a four-alarm fire.
A passerby reported the incident after seeing smoke in the area. Fire crews were actually training nearby, and were able to respond quickly, containing the fire.
Initially, firefighters were able to enter the vacant building to try to find the source of the fire, but it quickly escalated, according to Justin Stockman.
Eventually, the roof gave way to the weight of the fire and collapsed.
Fortunately, no one was hurt since the building was empty. The thick smoke has been the biggest impact, so far.
At times the smoke became so intense, it was nearly impossible to breathe as ABC7 News spoke with some of those workers watching the fire.
"All you could see was smoke pouring out of the second story windows, this is three stories...*coughs*... excuse me," choked Doug Herrick, who works nearby.
The building is surrounded by other office buildings.
Employees had been outside for hours watching the scene step by step.
"The building was just straight windows on fire when I got here and just recently I saw the balconies were kind of lifting up a little bit," said Martin Vazquez, who also works nearby.
Stockman says the situation went from an "offense" to a "defense" situation where firefighters had to battle the fire from outside the building.
The employees who work nearby told ABC7 News the building has been empty for several months. Santa Clara County officials confirmed to us that no one was inside at that the time, although it's unclear what type of commercial building it is.
"We did a primary search of this building in that first thirty minutes during the aggressive interior fire attack and again we had no occupants inside the building," said Brian Glass, acting chief of the Santa Clara County fire department.
Officials are asking the public to avoid the area as breathing any smoke from a building can be hazardous to one's health.
The fire is under investigation.
This story is developing. Check back for updates.