The incident was first reported at 8:46 p.m. while the store was still open, according to police.
Two employees were assaulted and one was pepper sprayed by the suspects, Walnut Creek place said.
Officers arrested two people, one of whom was in possession of a firearm. A third person was arrested nearby a short time later in possession of stolen Nordstrom property, police added.
A manager at a nearby restaurant says his stunned customers just watched as the thieves grabbed merchandise, loaded it in waiting cars and drove off.
That manager described the chaos.
"We probably saw 50 to 80 people in ski masks crowbars a bunch of weapons. They were looting the Nordstrom's right here. And I thought they were going to start beating cars. I had to start locking doors lock the front door lock the back door," PF Chang's manager Brett Barrette said.
A BMW convertible was stopped by police - believed to be somehow connected with the mayhem there.