Grocery group Ahold Delhaize will roll out small, automated warehouses to speed order picking and cut delivery times, Reuters has learned, as it revamps its ecommerce business in response to rising competition in a fast-growing sector.

At an investor event on Nov. 13, the world's eighth biggest food retailer is set to showcase a partnership that will allow it to automate order collection at mini "robot supermarkets" attached to the stores of its U.S. chains like Stop & Shop.

Now Netherlands-based Ahold Delhaize is teaming up with Takeoff, a start-up which builds small warehouses that stack groceries to the ceiling to save space and use robot arms to assemble shoppers' orders for items such as beer, milk, bread and fruit.