An investigation has revealed the deaths of a Polish mom and her seven-year-old son after they fell off a ferry final week was not an accident.

The pair had been travelling from Sweden to Poland when the mom dived overboard in a frantic bid to save her boy after he fell off the vessel into the icy Baltic Sea on Thursday.

They had been hauled from the water to a helicopter then transported individually to a Swedish hospital, however couldn't be saved.

Oessur Jarleivson Hilduberg, head of the Danish Maritime Accident Investigation Board, stated: "Our investigation showed quite clearly that it was not an accident."

Danish officers performed the preliminary investigation because the ferry, Stena Spirit, was crusing below its flag - which means the vessel is below Denmark's jurisdiction.

The investigation had collected knowledge from video footage, photos and witnesses, Mr Hilduberg stated.

Swedish prosecutors on Friday stated the case was being investigated as a potential homicide.

The baby is assumed to have fallen from a top of about 20m (65ft), in accordance with Swedish Maritime Administration spokesman Jonas Franzen.

Read extra:Lifeboats launched after fire breaks out on passenger ferry in the ChannelUp to 31 dead after passenger ferry fire in Philippines

The Stena Spirit had departed from Karlskrona in southern Sweden, round 310 miles (500km) from the capital Stockholm.

It was halfway by means of its journey to Gdynia on the coast of Poland, about 279 miles (450km) north of Warsaw, when the incident occurred.