A bizarre iceberg has been spotted by NASA scientists - in the shape of a near-perfect rectangle.

The tabular iceberg was floating among sea ice just off of the Larsen C ice shelf in the Antarctic.

NASA says the iceberg's sharp angles and flat surface "indicate that it probably recently calved from the ice shelf."

A photo posted by NASA shows a thick block of ice up to a mile long, dramatically protruding from a sea of thin frozen water.

It was discovered as part of the organisation's Operation Ice Bridge.

Using a fleet of research aircraft, it is documenting the Earth's polar ice to better understand connections between polar regions and the global climate system.

From yesterday's #IceBridge flight: A tabular iceberg can be seen on the right, floating among sea ice just off of the Larsen C ice shelf. The iceberg's sharp angles and flat surface indicate that it probably recently calved from the ice shelf. pic.twitter.com/XhgTrf642Z

— NASA ICE (@NASA_ICE) October 17, 2018

The decade-long airborne survey of polar ice studies annual changes in thickness of sea ice, glaciers and ice sheets.

Ice Bridge began flying in 2009 to maintain continuity of laser-altimetry measurements between NASA's ICESat missions.

The original ICESat mission ended in 2009, and its successor, ICESat-2, was launched this past September.

It is the first time that the Ice Bridge team survey the frozen continent, while NASA's newest satellite mission - the Ice, Cloud and land Elevation Satellite-2, ICESat-2 - studies it from space.

Ice Bridge is spending several weeks measuring changes in Antarctic sea and land ice, while flying under orbits of ICESat-2 to compare measurements.