The Danish vessel, which has capsized, will be salvaged by the Swedish coast guard and taken to Sweden because oil has started to flow into the water, Sweden’s TV4 said. It was not clear where the oil came from.
Several ships and helicopters were sent to the scene, authorities in Sweden and Denmark said.
According to the site marinetraffic, Scot Carrier was en route from Salacgriva in Latvia to Montrose in Scotland while Karin Hoej had left Sodertalje in Sweden for Nykoebing Falster in Denmark.
The cause of the collision was not immediately known but there was speculation it could have been due to poor visibility caused by fog.
“We do not know what happened yet. One of the ships has capsized and is upside down,” Jonas Franzen, press spokesman for the the Swedish Maritime Administration told Sweden’s Expressen daily.