Thieves have stolen a 17th-century Dutch painting valued at $1.25 million Cdn from the Art Gallery of New South Wales in Sydney.

Police suspect an inside job in the theft of A Cavalier by Baroque-era artist Frans van Mieris.

"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 oak panel, painted in oil, disappeared during daylight hours over the weekend, although it had been screwed to a wall.

The picture, of a man dressed in a feathered hat and frilled sleeves, is believed to be a self-portrait of van Mieris the Elder, the patriarch of a family of Dutch painters.

Police said they had questioned gallery staff about the theft, believed to have occurred between 10 a.m. and 12.30 p.m. local time on Sunday from a room that lacks security cameras.