An inmate has escaped from a Norwegian island prison famous for its liberal approach after sailing to shore using a surfboard and a toy shovel.

The 23-year-old man, who was convicted of rape and drug charges, remains at large, but is not thought to be considered a danger to the general public.

"The escape was discovered this morning, when we saw a window was open," Tom Eberhardt, manager of Bastoy prison, told VG newspaper.

"We had an old surfboard standing in a shelter, so old that it is almost an antique. This is what he has stolen, and he took a toy shovel as well."

Bastoy, situated on a picturesque one-mile square island just off the coast of Horten, south of Oslo, has established a worldwide reputation for its progressive and low-security approach to incarceration.

Bastoy has been described as 'the world's nicest prison' (Getty) (Getty Images)

Convicts hold keys to their own rooms – in wooden cottages rather than cells – and are unconstrained by the armed guards and fences that might be expected of an institution that houses inmates serving terms for murder, rape and other violent crimes.

Bastoy features tennis courts, a cinema room and a sauna, all designed to rehabilitate its residents and encourage them to live constructive lives upon their release.

The inmates perform jobs such as farming, fishing, or working in the island’s bicycle repair shop during their sentences.

A police officer confirmed the circumstances of the audacious escape to Norwegian state broadcaster NRK after the surfboard and spade were discovered near Horten.

"It sounds spectacular when it happens this way. But if it hadn't been a surfboard, it could have been something else. It's not so hard to find a floating device of some sort on the island," Eberhardt told Reuters.

Why the inmate would choose to break out of an institution once described by CNN as ‘the world’s nicest prison’ and ‘more like a resort than jail’ is unclear, but if the escapee is apprehended he is unlikely to be welcomed back to Bastoy.