A painting by Austrian artist Gustav Klimt that was stolen in 1997 might have been discovered hidden in a wall of the Italian gallery it was thought to have been stolen from.

Key points: The painting was thought to be stolen by fishing rod-wielding thieves in 1997

The painting was thought to be stolen by fishing rod-wielding thieves in 1997 But this week it was found hidden inside a secret compartment in the gallery wall

But this week it was found hidden inside a secret compartment in the gallery wall It's in excellent condition but experts are trying to work out if it is genuine

The story of the missing masterpiece, a portrait of a young woman completed in 1917 and valued at 60 million euros ($97 million), is considered one of the world's most baffling art mysteries.

It disappeared from the Ricci Oddi gallery in the northern city of Piacenza in February 1997, with police saying they believed thieves used a fishing line to hook it off the wall and haul it up through an open skylight to the gallery roof where the frame was discarded.

A skilled forgery of the painting, wrapped up and posted to a disgraced politician, was seized by authorities a month later, adding to the mystery.

But the story took another twist this week as a gardener cleared ivy off the gallery's outside wall.

Discovering a small trapdoor, he opened it to find what appeared to be the painting, inside a plastic rubbish bag.

"This is incredible," said Jonathan Papamarengh, head of culture in Piacenza town council.

A gallery spokesman said the building had been searched thoroughly when the painting was stolen. ( AP: Italian Police )

Police took charge of the find and experts will now examine it to check its authenticity.

Mr Papamarengh said it was hard to believe that the original had been hidden in the gallery wall ever since its disappearance, saying the building had been carefully searched after the theft.

"The painting's condition is excellent. It seems strange to believe it has been tucked away in a wall, close to the ground and vegetation for 22 years," he added.

Mr Papamarengh said the Klimt was second on the list of the most valuable art missing in Italy, just behind a painting by Michelangelo Merisi da Caravaggio that was stolen from a church in Sicily in 1969.

The Klimt is considered particularly important because shortly before its disappearance, an art student realised it was painted over another work previously believed lost — a portrait of a young lady that had not been seen since 1912 — making it the only "double" Klimt known to the art world.

ABC/wires