Using a track smashed by icebreakers, US cargo ships have sailed through Antarctic sea ice to offload supplies of food, fuel and equipment for scientific bases there.

The fuel tanker and the cargo ship docked at a pier in McMurdo Sound after following a 150km track cut through ice up to 3m thick.

The ice pack was nearly double its normal 77km width, after building up behind the world's biggest iceberg, known as B15A, which has blocked wind and water currents that usually break up ice floes.

Officials earlier feared the buildup might prevent the vessels crashing through to reach the pier.

Arthur Brown of the US National Science Foundation said the US icebreaker Polar Star and the Russian icebreaker Krasin encountered ice between 1.5m and 3m thick as they cut the channel.

The ships "had a bit of manoeuvring to do to get round B15A and its remnant pieces", Brown said. "But once that was done they had a pretty straight shot to open a channel up into McMurdo Station." He said a lot of people were surprised the ships had broken through so easily.

A US military tanker has already offloaded 34 million litres of fuel for the station's scientific base and New Zealand's Scott Base.

The supply ship American Tern is offloading enough supplies to support the scientific groups for the next 12 months. The vessel will then load containers of waste for disposal at sites in the United States.

McMurdo has a staff of about 1000 during the summer and about 100 remain for the harsh polar winter.

Scott Base has about 100 staff during summer and only about 12 in winter.

Mr Brown said the resupply operation was expected to be completed in the next three days.

Under the Antarctic Treaty, which controls the frozen southern continent, nations working there must remove all their waste products.

Three weeks ago scientists said B15A, a 160km-long iceberg, had run aground within 5km of slamming into a huge glacier known as the Drygalski Ice Tongue.

It also blocked paths to the sea for thousands of penguins, leaving up to 50,000 chicks to starve to death in the area this season.