LONDON — A major rescue operation is under way after two cargo ships collided in the Baltic Sea off the Swedish coast, causing one of them to overturn, BBC reported.

Two people were believed to be in the water following the incident in the early hours of Monday, the Swedish Maritime Administration (SMA) said.

The overturned ship, the Karin Hoej, is registered in Denmark. The other vessel is the UK-flagged Scot Carrier.

A spokesman for the SMA said screams were reported from the cold water.

"It is very cold and dark," Jonas Franzen told the BBC. "At the moment, the water is about 4C and the air is about 5C."

The two in the water were the only people on board the Karin Hoej when the incident occurred in an area of the Baltic Sea between the southern Swedish coastal town of Ystad and the Danish island of Bornholm, he said.

Franzen said a distress call was received at about 03:30 local time (02:30 GMT) on Monday. When a rescue team later approached the area, they reported "hearing screams in the water".

"We have not found anyone yet," he said, adding that divers were being sent out. Two helicopters and several boats from Sweden and Denmark have joined search and rescue efforts.

The Inverness-registered Scot Carrier is also assisting, with teams attempting to right the Danish ship and return it to a nearby port. All those on board the Scot Carrier are said to be safe and well.

The cause of the collision is not yet clear.

The Karin Hoej was heading to Nykobing Falster in southern Denmark after leaving Sodertalje, near Stockholm, in Sweden on Saturday. It was not carrying any cargo at the time of the incident.

The Scot Carrier was en route to the east coast of Scotland. It is not clear what cargo it was transporting or how many people were on board.

The Scot Carrier is 90m (295ft) long and the Karin Hoej is 55m, according to the maritime website VesselFinder.