WELLINGTON Ships in the south Pacific Ocean have been alerted that hundreds of icebergs believed to have split off Antarctic ice shelves are drifting north toward New Zealand, officials said Tuesday.

The nearest one, measuring about 30 yards tall, was 160 miles southeast of New Zealand's Stewart Island and was part of a 'flotilla' of icebergs that can be seen on satellite images, Australian glaciologist Neal Young said.

The alert comes three years after cold weather and favorable ocean currents saw dozens of icebergs float close to New Zealand's southern shores for the first time in 75 years.

New Zealand maritime officials have issued navigation warnings for the area south of the country.

'It's an alert to shipping to be aware these potential hazards are around and to be on the lookout for them,' Maritime New Zealand spokeswoman Sophie Hazelhurst said.

No major shipping lanes or substantial fishing grounds are in the area, but most ships there have little hull protection if they collide with an iceberg — which typically has 90 per cent of its mass under water.

On Monday, Rodney Russ, expedition leader on the tourist ship Spirit of Enderby, spotted a 500-foot-long iceberg about 60 miles northeast of Macquarie Island and heading north — about 500 miles south of New Zealand. Australian scientists reported another mass of 20 icebergs drifting north past Macquarie Island two weeks ago.

Young said satellite images showed the group of icebergs, spread over a sea area of 600 miles by 440 miles, moving on ocean currents away from Antarctica. One of the images alone had 130 icebergs and another had 100, he said.

Large numbers of icebergs last floated close to New Zealand in 2006, when some were visible from the coastline in the first such sighting since 1931.

It is rare for whole icebergs to drift so far north before melting, but a cold snap around southern New Zealand and favorable ocean currents have again combined to push the towering visitors to the region intact.

Icebergs are formed as the ice shelf develops. Snow falls on the ice sheet and forms more ice, which flows to the edges of the floating ice shelves. Eventually, pieces around the edge break off.

Young said that having the icebergs end up near New Zealand is not necessarily linked to global warming, but said that the rate of icebergs breaking off the Antarctic ice shelf in recent years may have increased due to dramatically rising temperatures on the continent over the past 60 years.— AP