By AppleInsider Staff

Published: 03:00 PM EST

Construction workers last week began to assemble a giant glass cube, which will be set like a jumbo gemstone atop Apple Computer's upcoming flagship retail store in the underground concourse of the General Motors building in Midtown Manhattan.

On Thursday workers operating a crane could be seen lowering several glass panels into place in the middle of the plaza of the GM building at 767 Fifth Avenue, between 58th and 59th Street.

When complete, the 32-foot glass cube will form a stunning gateway to a circular glass staircase and cylindrical elevator leading to an underground 25,000-square-foot Apple retail store.

Apple will reportedly reserve a few thousand square-feet for storage and office space, reducing the usable retail space to about 21,000-square feet -- almost the equivalent to its SoHo flagship retail store, located in southern Manhattan.

In a recent conference call, Apple for the first time acknowledged that it was constructing a giant retail store on 5th Ave. and said it hoped to begin operating out of the location in fiscal year 2006.

Sources privy to Apple's plans previously told AppleInsider the 5th Ave. store would rival anything seen from the company's retail division so far.

Apple reportedly began construction of the store in late-February.