This time, it was the auction house that went under the hammer.

A sledgehammer-wielding thief smashed his way into a Park Avenue auction house early yesterday and stole at least $100,000 in gold coins and jewelry, police sources said.

The crook broke the glass on the front door of Heritage Auction Galleries, on Park Avenue between 56th and 57th streets, at about 2 a.m.

A video camera caught him breaking open a case of gold coins, then forcing open another and snatching a bracelet. He was described as wearing a dark hooded sweatshirt, light-colored pants and dark shoes.