50 SHIPS ARE STUCK IN ICE IN THE BALTIC SEA

About 50 ships, including large ferries carrying thousands of people, are stuck in ice in the Baltic Sea, Swedish maritime authorities said.

"Around 50 commercial vessels are waiting for help from ice breakers (and) we have had as many as six large passenger ferries stuck, but have managed to free two of them," Johny Lindvall of the Swedish Maritime Administration's ice breaker unit said.

Mr Lindvall said he had not seen a situation with so many ships stuck at once since the mid-1980s.

Five of the six ferries stuck were shuttling passengers between Sweden and Finland, while the Regal Star ferry, which had been stuck since midnight local time on Wednesday (10am AEST Thursday), had been on its way to Estonia, he said.

Sweden's TT news agency first reported that the two largest ferries, the Isabella and the Amorella, were in total carrying 2630 passengers, but later revised the number to 1841.

The Isabella has been freed, while the Amorella and the Regal Star were among the ferries that are still stuck, Mr Lindvall said.

Viking Line head Jan Kaarstroem told TT that his company's ferries were well equipped to handle ice and that all the passengers were safe.

Two ice breakers are in the area where the ferries are stuck, while a third is on its way after helping commercial vessels further north in the Bay of Bothnia, Mr Lindvall said.