Two thieves posing as visitors to a Scottish castle overpowered a guide on Wednesday and stole a painting believed to be by Leonardo da Vinci, police said.
The Madonna with the Yarnwinder was taken from Drumlanrig Castle in southern Scotland, which is home to one of Scotland's richest landowners, the Duke of Buccleuch.
Police said the thieves overpowered a woman guide and made off with the painting at about 11am.
Officers said they were looking for four men seen driving a white Volkswagen near the castle at 11:15am. They also have released descriptions of two men seen near the castle at the time of the theft.
The painting, estimated by art experts to be worth around ?30 million (US$47 million), was hanging in a staircase hall of the castle, an area open to the public, when it was stolen.
"It has been here for more than 250 years," said the duke's son, the Earl of Dalkeith. "It's a remarkable work, a piece of great serenity and beauty upon which a great deal of scholarship has been carried out in recent years, identifying the fact that a considerable amount of it was by Leonardo himself and that the painting was created in his workshop."
According to the Drumlanrig Castle Web site, the artist completed the painting between 1500 and 1510. It said testing in the laboratories of the National Gallery of Scotland in 1986 produced evidence of its authenticity.
Experts at the gallery were not immediately available for comment.
Drumlanrig Castle, which houses one of the finest private art collections in Britain, also contains masterpieces by Rembrandt and Holbein.