When you order a jar of peanut butter or package of paper towels from Ocado — the world's largest online food retailer — chances are, it was picked by a robot.

Ocado has a total of three warehouses that deliver in the UK. They use robots, automated conveyor belts, shuttles, and cranes to pick up and carry food items at high-speed to trucks outside. The food is then delivered to customers.

The company's largest warehouses, located outside Birmingham and London, process over 1.3 million items per day, Ocado's CTO, Paul Clarke, tells Business Insider. The company will start construction on a fourth facility in 2018. It will measure approximately 563,000 square feet, making it one of the largest grocery warehouses in the world.

Though Ocado doesn't deliver as many food items as Amazon in the UK, it claims that its warehouses are more heavily automated than Amazon's.

"For grocery retail, Ocado has the most advanced automated warehouses in the world," Clarke says.

Take a look inside its robot-run facilities.