A trillion-tonne iceberg - one of the largest on record - has broken away from an ice shelf in Antarctica.

Researchers have been monitoring a huge crack in the Larsen C Ice Shelf, which had left a vast iceberg more than four times the size of London or a quarter the size of Wales "hanging by a thread".

Scientists announced on Wednesday that the rift had finally completed its path through the ice, causing the 2,200 square mile (5,800 square kilometre) iceberg to snap off.