Two freight ships collided off southern Sweden on Monday, with at least two people reported missing, Danish and Swedish authorities said.
One of the vessels capsized.
Media reports said the British-registered Scot Carrier and the Danish ship Karin Hoej had collided south of Ystad in Sweden, close to the Danish island of Bornholm.
Several ships and helicopters were sent to the scene, authorities in Sweden and Denmark said.
The cause of the collision was not immediately known but there was speculation it could have been due to poor visibility caused by fog.
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.
Jonas Franzen, spokesperson for the Swedish Maritime Administration, told Sweden's Expressen newspaper: "We do not know what happened yet. One of the ships has capsized and is upside down."
The Danish vessel 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.
The Swedish Coast Guard said it was carrying out an environmental rescue operation "to prevent oil or other harmful substances from being released into the sea" but said there "currently" were no ongoing oil spills.
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