The Swedish Maritime Administration says it received distress calls early Friday from the Langeland, and contact was lost shortly afterwards.
Helicopters and rescue boats have been sent to the area where the ship is believed to have gone down, in the Koster fjord near the Norwegian border. Rescuers say debris from the ship has been found there, but there is no sign of the crew members.
The maritime administration says the ship is 230 feet (70 metres) long and weighs 70 tons. It was on its way to Norway.