Amazon's automated attendants (pictures)

In a massive 1.2 million square foot warehouse in Tracy, Calif., more than 3,000 robots are helping Amazon keep up with customer's orders.

The Kiva robots, pictured here, are square, squat utilitarian machines. They're able to lift as much as 750 pounds, allowing them to bring shelves to the employees packaging orders.

There are now more than 15,000 Kiva robots in use at Amazon fulfillment centers in the United States. They have increased the capacity of the warehouse space, with the centers able to hold 50 percent more inventory using the Kiva system.

The Kiva robots have helped reduce processing times for some orders to mere minutes from several hours before.

Kiva robots travel through the warehouse, find appropriate products and deliver the entire shelf right to the human-staffed order-filling station.

The Kiva robots line up, and when it arrives, the employees -- called "pickers" -- selects the proper items from the shelf. Rather than the employees wandering through a massive warehouse to find an item, the shelf come right to them.

Dave Clark, Amazon's senior VP of worldwide operations and customer service, stands at a picking station alongside robot staffed mobile shelves.

Looking down at one of the 3,000 Kiva robots which swarm through the 1.2 million square foot Amazon fulfillment center in Tracy, Calif.

A look at the center eye on top of the Kiva robot, which aligns itself with the shelf, lifts it up, and carries the product-filled shelf to the order-filling "Picker."

The Kiva robots move quickly and silently through the warehouse, efficiently helping to fill orders.

This Tracy, Calif., fulfillment center also houses some Amazon Fresh grocery delivery operations, but that system has not been robotized, yet.

A look down the aisles of the 1.2 million square foot fulfillment centers. A seemingly endless maze, with Kiva robots patiently negotiating one another's paths.

Moving along a zipping conveyor belt, boxes ready for delivery are separated by destination, and loaded on to trucks for.

A Kiva robot lifts a shelf of goods just off the ground and moves through the warehouse to one of the order filling "picking stations."

Boxes rattle along conveyor belts, up ramps and down chutes on the path to order fulfillment. The loud drone of machinery fills the air, filling orders 24 hours a day, seven days a week.

Amazon says it plans to hire more than 80,000 seasonal workers this holiday season.