A maritime warning has been issued after about 100 icebergs were spotted south of New Zealand, some floating in a major ocean shipping lane, officials said.

A New Zealand air force P3 Orion maritime surveillance airplane on routine fisheries patrol in the southern ocean spotted the floating lumps of ice near Auckland Islands, 161 miles south of South Island.

The largest iceberg was about 1.2 by 0.9 miles and more than 425 feet high, said Orion captain Andy Nielsen.

While it was not unusual to see icebergs in the southern ocean, "we were surprised by the number of them and by how far north they were," he said.

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"We were operating in a major shipping lane and, due to the number of these things floating around, we thought it wise that Maritime New Zealand be informed," said Nielsen.

Brett Mullan, of the National Institute of Water and Atmospheric Research, said it was not unusual to see icebergs so far from the Antarctic coastal region.

He said the ice chunks likely broke away from Antarctica and circulated on westerly ocean currents as they drifted northward, pushed by a series of southerly storms.

Many of the icebergs were expected to melt as they drift further toward New Zealand's South Island, Mullan added.