An iceberg the size of Manhattan has broken off a glacier in Antarctica and could survive long enough to drift into international shipping lanes, scientists said Thursday.

A team led by British scientists has been monitoring the iceberg since it broke off the Pine Island Glacier in July in a bid to predict its path and environmental impact.

"An iceberg that size could survive for a year or longer and it could drift a long way north in that time and end up in the vicinity of world shipping lanes in the Southern Ocean," said Dr Robert Marsh, from the University of Southampton.

"There's a lot of activity to and from the Antarctic Peninsula, and ships could potentially cross paths with this large iceberg, although it would be an unusual coincidence," he said.

Icebergs that large -- Manhattan is 33 square miles (87 square kilometres) -- break off glaciers on average every two years, the scientists said.

The team's work will help track such drifting behemoths, which are likely to become more common as global warming encourages glacier "calving".

Large icebergs are not only a potential threat to shipping but also have an impact on the environment and could affect ocean currents.

"If these events become more common, there will be a build-up of freshwater which could have lasting effects," said Professor Grant Bigg from the University of Sheffield.