Five people have been rescued from an ice floe carrying a sauna tent, a motorised saw and an onboard motor after they lost control of their DIY vessel in the Stockholm archipelago.

Swedish authorities believe the passengers, who were German tourists, had been attempting to create their own motor-powered floating sauna when the swell from a passing passenger ferry broke the piece of ice and stranded them near Värmdö, an island near Stockholm.

The ferry’s crew rescued four people on Sunday, followed by a fifth who stayed longer to pack up their equipment, which included a sauna, a motorised saw, a standup paddle board, a Go-Pro camera and a boat motor.

Bemused passengers watched as the five figures stood in sub-zero temperatures on the disintegrating, narrow piece of ice, surrounded by water, against a backdrop of snow-covered rocks and pine trees.

Those rescued were returned to shore at the harbour village of Stavsnäs, according to authorities, apparently unharmed.

“We believe they had sawn loose an ice floe and gone out on it,” said Karolina Wichman, a spokesperson for Stockholm transport administration. “It was calm weather on Sunday, there was no wind. All vessels that pass through this area drive very calm and still. But ice is affected by boats in the area.”

Authorities in the area are accustomed to skaters getting into trouble on the ice and needing help in the winter, but this incident is believed to be the first of its kind.

“In Stockholm, and also wider Sweden, it is mostly ice-skaters who for different reasons end up in need of help at sea or fall through the ice. This was quite a spectacular sight,” said Wichman.

Johan Axberg, who witnessed the event from the ferry, told broadcaster SVT: “The boat drove carefully through the ice, but it was broken up by the waves and the ice floe drifted away. So the crew went out and started picking them [the tourists] from the ice floe, because the ice floe was breaking up more and more.”