Fifteen people were injured, several seriously, after an offshore wind crew transfer vessel hit a cargo ship in the German Baltic Sea, according to German authorities.

Lifeboat crew helped take those hurt off the World Bora following the collision at 0740 on Tuesday morning, said the German Maritime Search and Rescue Association.

The casualties from the offshore wind vessel were transported to hospital from the port of Sassnitz, some of the seriously injured by helicopter.

The World Bora was on its way to the 350MW Wikinger offshore wind farm operated by Spanish energy group Iberdrola, said the German authorities.

Iberdrola confirmed the vessel was on its way to Wikinger to carry out "ordinary operation and maintenance activities", with four crew and 11 wind farm technicians – two employees of Iberdrola itself and nine from turbine group Siemens Gamesa.

The Spanish group put the number of casualties at six. "Although, in principle, none of the injuries seem to be life-threatening, Iberdrola is following up on their condition.

"Iberdrola would like to express its gratitude to all the rescue teams involved in the operation for their diligence and professionalism," the company said in a statement.

There were no casualties on the cargo vessel involved, the 81-metre Raba which was travelling from Copenhagen to Szczecin in Poland.

German maritime police have launched an investigation into the incident.

World Bora, operated by World Marine Offshore, is a Windserver 30 design operated by World Marine Offshore, capable of carrying 24 passengers. The Trimaran was built in 2014.