SYDNEY, Australia - A 17th century Dutch painting valued at more than US$1 million was stolen from an Australian state gallery during viewing hours over the weekend, and police suspect an inside job, officials said Thursday.

"A Cavalier" by Baroque-era artist Frans van Mieris, disappeared from a small room in the Art Gallery of New South Wales. An oak panel painted in oil, the picture depicts a man believed to be the artist seated on a chair and dressed in a feathered hat and frilled sleeves.

"I am deeply shocked," gallery director Edmund Capon said. "Well over a million people visit the gallery each year and this is a very rare occurrence."

The room had no security cameras, but the 11-by-16 framed painting, insured for $1.17 million, was screwed to the wall, he said. Security measures were being reviewed.

Police said they had questioned gallery staff and one or more employees may have been involved in the theft, believed to have occurred between 10 a.m and 12:30 p.m. on Sunday. They estimated up to 6,000 people visited the gallery that day.

"The artwork was expertly removed from the art gallery wall," Police Superintendent Simon Hardman said.

An FBI expert said the painting would probably disappear for years if the thieves are not caught soon.

No reputable gallery or museum would buy the stolen work, meaning it would likely be bought by an unscrupulous private collector or remain in the hands of the thieves, Robert Goldman said.

"The FBI experience is that approximately 80 per cent of museum theft cases of art are inside jobs," Goldman told Australian Broadcasting Corp. from Philadelphia.