A three-kilometre slab of ice has broken off the Erebus glacier in McMurdo Sound.
The ice broke away from Antarctic glacier tongue that runs off Mount Erebus last month.
Antarctica New Zealand said each kilometre of ice would contain about five million tonnes and the chunk that broke away would supply Auckland with water for almost 100 years.
The manager of Antarctic science with Antarctica New Zealand, Ed Butler, said the iceberg is likely to become lodged opposite Mount Erebus in McMurdo Sound and would melt before it came anywhere close to New Zealand.
The Erebus glacier is thought to have calved three times in the 20th century.
Explorer Robert Scott observed that 4 kilometres of the ice broke off in a gale in March 1911. It was thought to have occurred again in the 1940s and was recorded a third time in 1990.