A storage system (100) is adapted to store a plurality of items and to load a delivery robot (2) with an item. The storage system (100) includes a delivery robot level (110), at least one storage level (112, 114, 116, 118) for storing the items, and a loading robot (130) adapted to grip the items and to load the items from a storage level (112, 114, 116, 118) to a delivery robot (2) located on the delivery robot level (110). The storage system (100) is adapted to move the items within a storage level (112, 114, 116, 118). The storage system may be provided with wheels and thus be mobile. It may be loaded onto a vehicle for transport from a loading area where the storage system is loaded with items for delivery, to a delivery area where the items are to be delivered by one or more delivery robots.