Two cargo ships collided on Monday in the Baltic Sea between the Danish island of Bornholm and the southern Swedish city of Ystad, the Danish Defence’s Joint Operations Centre said on Monday.
One ship was registered in Denmark, and the other was British.
The Danish ship appeared to be upside down. It had two people on board and their status was not known, the centre said.
The British ship was still functional and the crew was safe, it said.
The incident happened in Swedish territorial waters and Denmark was helping Swedish authorities with the rescue. A rescue boat has been launched from Bornholm island and a helicopter had also been dispatched from the Danish side.
Swedish news agency TT cited a Swedish coastguard spokesman as saying one of the vessels was 90 metres long and the other was 55 metres.