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A giant flotilla of 100 icebergs is passing just 260km off the coast of the South Island - the closest the glacial masses have been to this country for 70 years.

Dramatic pictures taken yesterday show the largest of the icebergs stretches 2km and towers 150 metres above the sea.

Mike Williams, physical oceanographer at the National Institute of Water and Atmospheric Research, said it was the closest recorded iceberg to New Zealand since 1931.

"It's very rare for them to be in a place where they might come close to the South Island," he said.

An Air Force crew on a routine fisheries patrol saw the icebergs, concentrated in two large groups, in the Southern Ocean.

Squadron Leader Andy Nielsen said that, although it was not unusual to see icebergs in the Southern Ocean, he was surprised by the number and how far north they were.

Auckland University glacial geomorphology lecturer Dr Paul Augustinus said last night that it was unusual for icebergs to travel that far north from Antarctica.

But it was unlikely to be related to global warming. "I wouldn't like to speculate on the cause ... It could relate to a number of factors such as the break-up of a larger iceberg."