Rescue helicopters have been searching for Dominick Arduin

French-born Dominick Arduin began her expedition in northern Siberia on Friday, in a bid to become the first woman to reach the pole unaided.

Her support team have received no word from her and a helicopter search has so far failed to locate her.

Her assistant Pirkko Salonen said it was the longest time that the 43-year-old explorer had been out of contact.

"It looks quite bad, but we're still hoping that no news is good news," she told the BBC.

"We're worried, but at the same time we're hoping that it's just a mechanical fault."

Frostbite

Ms Arduin was born in France, but now has Finnish citizenship after living in Lapland for the past 15 years.

Last year, in a previous attempt to reach the North Pole, she fell into freezing water and had to have her toes amputated after suffering frostbite.

She began her latest expedition by rowing across a 55km (34-mile) stretch of the Arctic Ocean to reach firm ice.

From there, she planned to continue on skis.

Ms Arduin had intended to make daily contact by satellite telephone, but her support team have not heard from her since she set out.

The only indication of her whereabouts came on Saturday, when they received a signal from a satellite beacon pinpointing her location.

Ms Salonen said rescue helicopters had searched for her on Tuesday until darkness fell and would resume the hunt at 0300 GMT.