Photo of the rift. Photo: NASA

One of the biggest icebergs in history has snapped off the West Antarctic ice shelf, according to scientists who have been monitoring a growing crack for months.

Satellite images confirmed that the trillion-tonne iceberg had broken away and was adrift at sea.

“The calving occurred sometime between Monday, July 10 and Wednesday, July 12, when a 5,800-square kilometre section of the ice shelf finally broke away,” the Swansea University said in a statement on Wednesday.

The massive sheet of ice with an area nearly as large as the size of the US state of Delaware had been developing a crack across the Larsen C ice shelf over the past few years.