It's taken roughly five months, but a massive iceberg has separated from Antarctica's Pine Island Glacier. According to NASA's Earth Observatory, the estimated size of this iceberg, named B-31, is around 660 square kilometres (33 km long by 20 km wide) – a city-sized block of ice that has slowly migrated away from the continent, and is now floating out to sea. Take a look at some massive icebergs afloat in the oceans.

The B-31 Iceberg is seen after separating from a rift in Antarctica's Pine Island Glacier in this NASA Earth Observatory handout image acquired on November 13, 2013. Scientists are monitoring an unusually large iceberg – roughly six times the size of Manhattan – that broke off from an Antarctic glacier and is heading into the open ocean, although not in an area heavily navigated by ships. (Photo by Holli Riebeek/Reuters/NASA Earth Observatory)

File photo of an iceberg floating near a harbour in the town of Kulusuk, east Greenland August 1, 2009. (Photo by Bob Strong/Reuters)

A whale dives into sea off the coast of Greenland's capital Nuuk October 17, 2012. (Photo by Alistair Scrutton/Reuters)

Adelie penguins stand atop ice near the French station at Dumont d'Urville in East Antarctica January 22, 2010. (Photo by Pauline Askin/Reuters)

Calved icebergs from the nearby Twin Glaciers are seen floating on the water on July 30, 2013 in Qaqortoq, Greenland. (Photo by Joe Raedle/Getty Images)

A large iceberg melts into jagged edges as it floats in Eriks Fjord near the town of Narsarsuaq in southern Greenland July 26, 2009. (Photo by Bob Strong/Reuters)

Ships are seen among the icebergs that broke off from the Jakobshavn Glacier as the sun reaches its lowest point of the day on July 23, 2013 in Ilulissat, Greenland. (Photo by Joe Raedle/Getty Images)

A fishing boat navigates past icebergs that broke off from the Jakobshavn Glacier on July 23, 2013 in Ilulissat, Greenland. (Photo by Joe Raedle/Getty Images)

A boat is seen seen among the icebergs that broke off from the Jakobshavn Glacier as the sun reaches its lowest point of the day on July 23, 2013 in Ilulissat, Greenland. (Photo by Joe Raedle/Getty Images)

Calved icebergs from the nearby Twin Glaciers are seen floating on the water on July 30, 2013 in Qaqortoq, Greenland. (Photo by Joe Raedle/Getty Images)