An ice shelf in western Antarctica has begun to collapse in what scientists yesterday warned was the latest evidence of rapid climate change in the region.

The 5000-square mile Wilkins ice sheet is the largest on the Antarctic Peninsula to be threatened with collapse, and is "hanging by a thread", the British Antarctic Survey said. This comes as a result of global warming, according to scientist Professor David Vaughan.

While icebergs naturally break away from the mainland, collapses like this are unusual but are happening more frequently in recent decades, he said.

The collapse is similar to what happens to hardened glass when it is smashed with a hammer.

Because scientists noticed satellite images within hours, they diverted satellite cameras and even flew a plane over the continuing collapse for rare pictures and video.

Images released by the US National Snow and Ice Data Centre showed that an iceberg the size of the Isle of Man (25.5 miles by 1.5 miles) broke off on February 28.

This was followed by disintegration of around 220 square miles of the interior of the shelf and crumbling of the edges in what the centre described as a pattern "characteristic of climate-induced ice shelf break-ups".

"It's an event we don't get to see very often," said Ted Scambos, lead scientist at the centre in Boulder, Colorado. "The cracks fill with water and slice off and then topple. That gets to be a runaway situation."

A large section of the shelf, a broad plate of permanent floating ice around 1000 miles south of South America, is now held together by a narrow 3.7-mile strip of ice shelf between two islands.

The collapse of the ice shelf had been predicted but is happening more quickly than expected, the scientists said.

They added that they are not concerned about a rise in sea level from the latest event but maintain it's a sign of worsening global warming.

It is thought warming of the atmosphere, which has been happening several times faster on the Antarctic Peninsula than the global average in the past 50 years, has created more surface melt of ice which is weakening the shelf.

Vanishing sea ice has left the shelf exposed to the action of ocean waves which could also be having an effect.

Mr Vaughan, who predicted in 1993 that the northern part of the Wilkins ice shelf would be lost within 30 years, said: "Wilkins is the largest ice shelf on the Antarctic Peninsula yet to be threatened. I didn't expect to see things happen this quickly.

"The ice shelf is hanging by a thread - we'll know in the next few days or weeks what its fate will be."

While the summer melt period in Antarctica is coming to an end, making it unlikely that there will be further collapse before next year, Mr Vaughan warned that a major storm in the coming days could accelerate the disintegration.

He added: "Climate warming in the Antarctic Peninsula has pushed the limit of viability for ice shelves further south, setting some that used to be stable on a course of retreat and eventual loss.

"The Wilkins breakout won't have any effect on sea level because it is floating already but it is another indication of the impact that climate change is having on the region."

The Wilkins ice shelf covered more than 6000 square miles, the size of Northern Ireland, but began to retreat in the 1990s.

The threat to the ice sheet follows the total collapse of other shelves in the Antarctic, including most famously the Larsen B ice sheet which went in 2002.