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 and was being towed to a Swedish port.

The Swedish Maritime Administration said the British-registered Scot Carrier and the Danish ship Karin Hoej collided south of Ystad in Sweden, close to the Danish island of Bornholm.

The Danish ship had capsized and was floating upside down.

At least 11 vessels, one airplane and one helicopter took part in a search for the missing crew members, but the administration said it had now “ended its search operation at sea for the two missing persons in the water” and that the pair had not been found.

The capsized vessel was being towed closer to land where divers from the Swedish Armed Forces and the coastguard, among others, would search it. Police also planned to take over the case and examine the ship.

“We have no idea when the work can be completed”, the maritime agency said in a statement.

Swedish Coast Guard prosecutor Jonatan Tholin said prosecutors had opened a preliminary investigation on potential charges of gross negligence in maritime traffic and “gross sea drunkenness”.

But the cause of the accident remained unclear, the administration said. At the time, fog caused poor visibility in the area.

Meanwhile, 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” and that there were currently no ongoing oil spills.

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