The ice chunk, measuring some 700 meters (2,300 feet) long with an estimated depth of 350 meters, caused a stir when it was sighted by experts based on Australia's remote Macquarie Island.

“I've never seen anything like it - we looked out to the horizon and just saw this huge floating island of ice,” said fur seal biologist Dean Miller.

Australian Antarctic Division glaciologist Neal Young said the flat-topped slab could break into dozens of smaller icebergs as it moves in the direction of New Zealand, causing a possible shipping hazard.