A "perfect" diamond said to be so large that it draws awe-struck people across a room has sold for $22 million at a Sotheby's auction in New York.

The 100-carat, emerald cut, D color, internally flawless diamond is the largest of its clarity and cut to ever be shown at auction.

"People everywhere have been drawn to it from across the room and they are in awe of its size, particularly when they put it on their hand," said Gary Schuler, the head of Sotheby's jewelery department in New York, before the sale. "They can't believe there's a diamond this pure of such impressive scale."