Meet Amazon's newest holiday workers, the Kiva robot. At this fulfillment center in Tracy, California, more than 3,000 of them cruise the warehouse floor helping employees fill millions of orders. The little orange robot goes out and picks the right pod of inventory, and brings it back just at the right time for the person to pick the item out to go in that customer shipment. [INAUDIBLE] Before the Kiva robots, the workers used to walk the warehouse aisles picking up the items. But now, they stay on these platforms, and the robots bring the shelves and the items directly to them. The 320-pound robots can lift up to 750 pounds. They have motion sensors to detect objects in their way, and can travel between three and four miles per hour. Amazon says the robot's small footprint allows it to squeeze in 50% more inventory into this warehouse, which is the size of 59 football fields. They've also improved efficiency by 20% so it only takes 15 minutes to fill some orders instead of 90. On Cyber Monday last year, Amazon customers ordered 426 items every second. Amazon expects that number to be bigger this cyber monday. The process at an Amazon fulfillment center starts when products arrive by the truckload. The items are sent up to one of the four floors where Kiva robots operate. In this new generation fulfillment center we have associates who are taking products off the carts and putting them onto the shelves that are moved by our Kiva robot. A worker finds a space to stock the item on one of the moving shelves. It doesn't matter if there are paper towels next to board games. Just as long as the robots know where to find it among the 21 million items. Then, the robots wait to retrieve the item when someone places an order. From there, items are handpicked and whisked away on miles of conveyor belts. [NOISE]. To be sorted, packed and shipped. There's even a robot that folds the shipping boxes. While some may worry about robots taking jobs away from humans, Amazon insists that is not their intention. You're gonna see there's 4,000 people working in this building. Even with all the automation that's in place here, that's because our focus on automation is about helping people to do their jobs, not replacing people. So far 10 of the 50 Amazon fulfillment centers in the United States have integrated the Kiva robots. In Tracy, California, I'm Kara Tsuboi, for CBS News.