Six empty containers were washed overboard from a cargo ship west of the Fair Isle Channel on Friday night.
The coastguard says there has been no sign of the containers, which eash measured 20 feet in length, since the incident took place.
A warning has gone out for vessels to be on the look-out for them.
The containers fell from the Marmaui container ship in harsh conditions between 8pm and midnight on Friday. The vessel was heading from Iceland to Rotterdam when the incident happened.