An iceberg two-thirds of the size of Toronto has broken away from an Antarctic ice shelf, leaving the shelf in danger of imminent collapse, scientists with the British Antarctic Survey said Tuesday.

The berg is still moving, leaving a large part of the Wilkins Ice Shelf on the Antarctic Peninsula supported only by a thin strip of ice hanging between two islands.

Glaciologist Ted Scambos from the University of Colorado first raised the alarm over the ice shelf, and colleagues at the British Antarctic Survey recently sent a small plane on a reconnaissance mission to check out the extent of the breakaway from the shelf. They confirmed that the shelf broke away sometime over the past few days.

In 1993, Professor David Vaughan of British Antarctic Survey predicted the northern part of Wilkins Ice Shelf was likely to be lost within 30 years if climate warming on the peninsula were to continue at the same rate. Climate warming increases the volume of summer meltwater on glaciers and weakens ice shelves.

"Wilkins is the largest ice shelf on the Antarctic Peninsula yet to be threatened. I didn't expect to see things happen this quickly," Vaughan said in a release. "The ice shelf is hanging by a thread — we'll know in the next few days or weeks what its fate will be.

The Wilkins Ice Shelf covered an area of 16,000 square kilometres (the size of Northern Ireland). It was stable for most of the last century but began retreating in the 1990s. A major breakaway occurred in 1998, when 1,000 square kilometres of ice were lost in a few months. A collapse of the shelf is not expected to have any effect on sea level because it is already floating.

Antarctica has experienced unprecedented warming over the past 50 years. Several ice shelves have retreated in the past three decades, with six of them collapsing completely.

The U.K. government-funded British Antarctic Survey researches global environmental issues.