A trillion-tonne iceberg, one of the biggest on record, has snapped off the West Antarctic ice shelf, said scientists Wednesday who have monitored the growing crack for months, AFP says.

"The calving occurred sometime between Monday, July 10 and Wednesday, July 12, when a 5,800-square kilometre (2,200-square mile) section of Larsen C (ice shelf) finally broke away," the Swansea University said in a statement.