The Swedish Maritime Administration said on Thursday that about 50 vessels are stuck in the thick ice in the Baltic sea off Sweden's east coast.

A handout photo released by the Swedish Coast Guard shows a large cargo ship stuck in the ice in the Baltic Sea. [Xinhua/AFP]

Among the vessels, there are six large passenger ferries which are in total carrying more than 2,000 passengers, the administration said in a statement.

Two of the ferries, including the large Isabella passenger ferry carrying 1,322 passengers and crew, have been freed.

Four other vessels, including the Amorella, another passenger ferry with 753 passengers and 190 crew members aboard, are still stuck.

The administration has sent all the ice breakers in the area to free the ferries, but gale-force winds are hampering the effort.

No one is hurt and there are no immediate plans to bring people off the ferries, but helicopters and military hovercraft are on standby in case evacuations become necessary, the administration added.

Sweden has suffered an unusually harsh winter this year, with temperatures across the country almost continuously lying well below freezing since December.