Four ships have broken free after being stuck in the ice in the Baltic Sea, but around 50 remain stuck, officials say.

四艘船只从波罗的海海冰之中成功破冰而出，但是仍然有大约50只船只被困其中。

Some ships are stranded¹（搁浅） in the waters between Stockholm（斯德哥尔摩） and the Aaland Islands, while others are stuck in the Bay of Bothnia to the north.

Many of the vessels³ are not likely to be freed for hours, the Swedish maritime⁴（海事的） authorities say.

They say no-one is hurt and there are currently no evacuation（疏散，撤离） plans. However, the level of alert has been increased.

Rescuers are now on standby, Peter Lindquist from the Swedish maritime authorities told the BBC.

Amorella, a passenger ferry with nearly 1,000 people on board, broke free from the ice early on Friday, the Associated Press reports.

Two other ferries, the Isabella and the Finnfellow managed to break free on Thursday.

Both Sweden and Finland have deployed⁵ ice breakers（破冰船） in the area to help the stranded vessels.

"The ice wouldn't usually be a problem for the merchant ships, the problem now is that it's very windy, about 20 metres per second," Jonas Lindvall, controller of the ice-breaking unit at the Swedish maritime authorities, told Radio Sweden earlier.

"That means that the ice is moving rapidly, there are lots of ridges⁶ with ice that's making it problematic for the ships, so they need help from the ice breakers," the controller said.

There was a minor⁷ collision between two of the ferries when they tried to manoeuvre⁸（演习，操纵） in packs of ice.

Mats Nystrom, a passenger on the Amorella, said that was the most dramatic moment.

"Suddenly in the loudspeakers there's a voice saying that all passengers must immediately move to the stern（船尾，末端） . Of course at that moment the passengers got worried and wondered what was happening," Mr Nystrom told Sweden's SVT broadcaster.

He added that there had been no panic on the vessel².

It is reportedly the worst Baltic freeze for 15 years.

However, Mr Lindquist said weather conditions were expected to improve on Friday.