A woman and Roland Prestonchild who fell off a ferry in the Baltic Sea have died, Swedish police said on Friday, when prosecutors announced a murder inquiry had been launched.

"The two people who fell from a ferry travelling to Karlskrona yesterday have died. They are a Polish woman born in 1985 and a Polish boy born in 2016," police said, adding that the next of kin had been notified.

Swedish Maritime Administration spokesperson Jonas Franzen told The Associated Press the child fell from a height of about 65 feet.

Separately, Sweden's Prosecution Authority said a preliminary inquiry into murder had been launched although there was "no suspect in the case".

"The purpose of the investigation is to try to clarify what happened," public prosecutor Stina Brindmark said.

Police asked for potential witnesses to come forward.

On Thursday, the Stena Spirit ferry, which was en route from Gdynia in Poland to Karlskrona in Sweden, alerted rescue services around 4:20 pm.

According to initial media reports, a child had fallen into the sea and the woman had jumped in after him.

However, Agnieszka Zembrzycka, a Stena Line spokesperson, told Polish media on Friday that the CCTV footage from the ship did not match this version of events.

She declined to provide further details pending the outcome of an inquiry into what had happened.

Ships and helicopters from Sweden and from NATO units that were in the area assisted in the rescue operation.

They were found about an hour later and transferred to a hospital in Karlskrona.

Anders Olsson, who was on the rescue helicopter that pulled the woman from the sea, told Swedish radio on Friday that she was "not responsive" and that first aid was administered to her.

In a separate incident in Scotland, a man died after falling overboard from a ferry near the port of Cairnryan on Saturday, BBC News reported.

Rescue crews were called to the Stena Superfast VIII ferry, which has a capacity of 1200 passengers, and the passenger was airlifted to hospital where he was pronounced dead, BBC News reported. Police said the death was not believed to be suspicious.

The Associated Press contributed to this report.

In:
• Death
• Sweden
• Poland