Authorities in South Africa say they are preparing to rescue more than 100 people - including 79 Russian scientists - whose ship is trapped by frozen seas in Antarctica.

The German ship, named the Magdalena Oldendorff, was returning from a Russian research base on Antarctica's Princess Astrid coast, when thick ice blocked its escape route.

A South African ship will leave Cape Town for Antarctica on Sunday to provide food and fuel to the stranded passengers.

Argentine and Russian ice-breaking vessels are also expected to join the rescue attempt.

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An official in the South African Government's Antarctica programme has told the BBC that the trapped Russian scientists are in good health, but not in good spirits.

Both South Africa and Russia send scientists to Antarctica

Their ship is currently in open water but their escape route out of Antarctica is blocked by ice.

South African Defence Force spokesman Colonel Piet Paxton told the French agency AFP that the ship had got stuck near the base for the South African National Antarctic Expedition.

The South Africans say they usually like to get their ships out of Antarctica by April at the latest, but they say the Russians are known to take risks.

Rescue party

The South African rescue ship Agulhas is due to team up with the Argentine ice-breaker Almirante Irizar for the rescue mission.

It may be that this ship will be able to force its way through the ice and therefore create a passage to allow the Russians out.

Col Paxton said the helicopters on the South African ship would be used to take the standed passengers from the trapped vessel onto the ice-breaker and the Agulhas.

"But this time of the year it's dark there [24 hours a day], and temperatures drop to -50C, which basically makes this a night operation and flying extremely difficult," Col Paxton said.

But he insisted that those on board were not in danger.

"This is not a serious situation. We believe there is enough food on board," he said.

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