A huge iceberg expected to be one of the biggest ever recorded is poised to break off Antarctica, changing the landscape of the frozen continent, scientists say.

The massive sheet of ice with an area of almost the size of the US state of Delaware has been developing a crack across the most northern ice shelf, Larsen C on the Antarctic Peninsula, over the past few years.

Ice shelves are areas of ice floating on the sea, several hundred metres thick, at the end of glaciers.

According to scientists at the Project Midas at the University of Swansea in Wales, the iceberg expanded abruptly last month, growing by about 18km on top of its existing 80km length. It is expected to snap if it expands a further 20km.

"The Larsen C Ice shelf in Antarctica is primed to shed an area of more than 5,000sq km following further substantial rift growth," the scientists said in a statement on Friday.

The iceberg "will fundamentally change the landscape of the Antarctic Peninsula" and could herald a wider break-up of the Larsen C ice shelf, the statement said.

Scientists fear the loss of ice shelves around the frozen continent will allow glaciers inland to slide faster towards the sea as temperatures rise owing to global warming, resulting in the rise of world sea levels.

The European Union's Copernicus Climate Change Service said on Thursday that last year was the warmest on record by a wide margin, stoked by greenhouse gases and an El Nino weather event that released heat from the Pacific Ocean.

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Several ice shelves have cracked around northern parts of Antarctica in recent years, including the Larsen B which disintegrated in 2002.

Andrew Fleming, remote sensing manager at the British Antarctic Survey, who also tracks Larsen C, said the ice was being melted both by warmer air above and by warmer waters below.

In some cases, big icebergs simply float around Antarctica for years, causing little threat to shipping lanes as they melt. More rarely, icebergs drift as far north as South America.

"The Larsen B shattered like car safety glass into thousands and thousands of pieces. It disappeared in the space of about a week," said Fleming.

In November 2015, almost 200 nations reaffirmed plans to combat climate change as an "urgent duty". There has been concern that US President-elect Donald Trump will try to undo a hard-won global accord for limiting greenhouse gas emissions.