A MASSIVE crack is growing wider in the Antarctic ice sheet and could break apart in coming months, forming a gigantic iceberg, warn NASA scientists.

The crack in western Antarctica's Pine Island Glacier stretches for at least 30 kilometres and runs 50 metres deep.

NASA's image of the crack spreading at a rate of two metres a day on the Pine Island Glacier. Credit:AFP

The rift is widening at a rate of two metres a day, said NASA project scientist Michael Studinger. When the ice breaks apart, it will produce an iceberg more than 880 square kilometres, said Mr Studinger, who is part of the US space agency's IceBridge project. But the process is not a result of global warming, he said.

''We expect that later this year or early next year there will be a pretty large iceberg forming as part of a natural cycle,'' he added.