Rescuers are using a break in harsh winter conditions to airlift Russian scientists from a research ship trapped in ice off Antarctica and deliver half a tonne of supplies to those remaining on board.

Two helicopters flew from the heated deck of South African research ship Agulhas that has penetrated the ice fields to within 350 kilometres (190 nautical miles) of the trapped vessel, Magdalena Oldendorff.

The Agulhas has been sailing through extreme weather

The Oryx helicopters airlifted 21 scientists from the Magdalena on Thursday and will try to rescue another 44 on Friday.

The window of slightly more moderate weather, with temperatures minus 15 degrees Celsius, is expected to close on Saturday.

"The Agulhas is in about 10 to 15 centimetres of ice at the moment, but that will thicken quickly so the captain will sail north on Friday," said Tanya Hacker, spokeswoman for the Cape Town-based rescue mission.

For each helicopter to make the two journeys, Friday's mission will have to begin before first light and end after twilight of the short (six-hour) Antarctic daytime.

Longed-for supplies

If things goes according to plan, 14 scientists will be left on board along with the 38-member crew.

Rescuers hope to airlift the remaining scientists and 11 non-essential crew members during the next break in the weather.

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The first relief flight carried yeast and flour, cigarettes, coffee and 90 kilograms of sugar to meet the most urgent needs.

Temperatures are expected to fall again before Saturday

The second flight carried camembert and cheddar cheese, veal sausages, potatoes and oranges to liven up the diet of the men staying aboard.

The stranded scientists and crew began rationing their remaining food last week.

"We wanted to give them everything that they had on their request list, as what was important was to boost morale," Ms Hacker told BBC News Online.

"This is a sad day and a happy day for them, as these men are being split up after spending between 15 and 18 months together," she said.

Icebreaker

On Tuesday an Argentine ship Almirante Irizar set off to break a path through the ice to the trapped vessel, so the Magdalena can make its way out under its own steam.

The Almirante is expected to arrive on 7 July. Essential crew members will remain on board the Magdalena until then.

The Magdalena Oldendorff had been heading back to Cape Town before a massive ice drift blocked its way early in June and forced it to retreat and call for help.

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