Antarctic experts in New Zealand have raised concerns that the iceberg, some 150 kilometres (95 miles) long and 25 kilometres (15 miles) wide, would block supply routes to three polar ice bases and lead to the deaths of tens of thousands of penguins.

The iceberg, known as B15A is a remnant of one of the biggest recorded yet, which "calved" off the Ross Ice Shelf in 2000 and began breaking up last year.

Its bulk has disrupted air and water currents that normally break up pack ice at this time of year in McMurdo Sound, the main maritime access route to three Antarctic bases run by New Zealand, the United States and Italy.

John Cockrem, a penguin researcher at New Zealand's Massey University, said two colonies of Adelie penguins on Ross Island were also at risk because the iceberg's presence meant they had to travel up to 60 kilometres (35 miles) to find food in open waters.

But Julian Tangaere, the manager of New Zealand's Scott Base, said the iceberg was moving out to sea at a rate of two-to-three kilometres (more than a mile to two miles) a day, leaving an increasingly wide, ice-filled gap to the open ocean.

"To be honest I think a few people have hit the panic button and I think there's plenty of time yet to wait and see how things develop," he told AFP by telephone from Antarctica.

Tangaere said temperatures in the area had been "pretty warm" at two degrees Celcius (about 35 degrees Farenheit), softening the pack ice through which four supply vessels will have to travel to reach the three bases in the New Year.

"Our expectation is that it's going to be a tough job, but it won't prevent the supply ships from getting in," Tangaere said.

"But given that it (the iceberg) has been here for some years and supplies have always reached us before you'd have to say our chances of success are certainly higher than those of failure."

Cockrem said the at-risk Ross Island penguin colonies contained about 50,000 breeding pairs, less than two percent of the breeding stock of Adelie penguins in Antarctica.

"While it's a critical issue for those particular penguins, it's not in terms of the survival of the species," he said.

"It's worth noting that this is a natural phenomenon, in terms of the presence of the iceberg. It hasn't been seen recently but these things happen in Antarctica."

Greenpeace New Zealand said it was unclear whether the iceberg was caused by global warming but its presence highlighted the need to improve knowledge about climate change.

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