A door block (9) serving for blocking a door (2), which is side-hinged on a casing (3) around an opening in a container wall, against being opened by unauthorised persons. The door block comprises a rotatable closing rod (5), a handle (6) on the closing rod and a cam (7) fitted on the closing rod for engaging a keeper (8) on the casing when the door is closed and the closing rod rotated into closed position by means of the handle. The door block furthermore comprises a, seen in cross section, mainly U-shaped covering (14) having a body (16) and two flaps (17) projecting from this body, and in the blocking position extending across the closing rod with a piece of this rod located in flushing cuts (18) in the flaps and the handle encompassed between the body and the flaps; a catch hook (19) pivotally mounted in the covering for locking the closing rod in the cuts of the flaps by means of a projection (26) on the catch hook; and a lock (13) for locking the catch hook in its locking position. The door block has a simple and effective structure. It is easy to apply as it does not require any use of tools nor any kind of manipulation in the structure of the respective door. It is furthermore difficult to break open, and a possible burglary is clearly revealed by the condition in which the door block will be left by the burglary.