12 of the ships are stuck outside Sundsvall with the remaining eight outside Gävle.
Cecilia Wegnelius from the Swedish coastguard told TT that she couldn't speculate on how long it would take to break the ice and free the ships.
"I cannot say. New ships are getting stuck all the time. I've worked on an icebreaker myself and we've been out even in May."
A SCA forestry owned freighter Ortviken is one of those affected. The ship is stuck outside Sundsvall, one of the areas worst affecred by thick ice. SCA exports paper from Sundsval, via Umeå to the German port of Hamburg.