STOCKHOLM, SWEDEN - Icebreakers on Friday freed dozens of ships, including passenger ferries, that had been trapped, some for several days, in thick Baltic Sea ice, Swedish authorities said.

'There are no more ships stuck in the ice,' Ann Ericsson of the Swedish Maritime Administration's ice breaker unit, told AFP.

All the vessels became stuck just outside the Stockholm archipelago Thursday, including the ferry, the Amorella, carrying around 1,000 passengers and crew. It also broke free on Friday, Ericsson said.

Many cargo ships and commercial vessels had been trapped further north in the Bay of Bothnia, and the maritime administration said Thursday about 50 ships were stuck in the Baltic ice.

Twelve ships were still waiting in port near the central port of Sundsvall for an ice breaker, which had been sent to help the trapped ferries late Thursday, to return to escort them out, according to Ericsson.

'They're waiting for help, but none of them are stuck,' she said.

The Amorella collided with another trapped ship while trying to free itself from the ice, but the Viking Line said no damage was done to the ship and that there had at no time been any danger to the passengers.

Passengers on the Amorella were requested to move to the front of the boat to avoid any collision impact, according to Mats Nystroem, one of the passengers.

The two ships 'were simply drifting towards each other,' the Amorella passenger said told Swedish public radio from the stranded ferry.

Another passenger, 55-year-old Rigmor Okoli, said it was frightening just drifting out on the Baltic Sea.

'It is so dark everywhere,' she told the Expressen tabloid's online edition. 'We have no idea how or when we'll get home.'

The Swedish Maritime Administration issued a warning to ships not to take the route where most of the ferries became stuck. Freezing winds whipping over the area pushed thick ice towards the coast, Johny Lindvall, also of the Swedish Maritime Administration's ice breaker unit, told AFP Thursday.

'They got caught outside the archipelago, where there is moving ice. It's hard to navigate,' he said, adding that he had not seen so many ships stuck at once since the mid-1980s.

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