Nancy Wake, the French Resistance fighter who became Australia's most decorated World War II heroine, has died in a London hospital at the age of 98.

Born in New Zealand and raised in Sydney, Ms Wake was nicknamed "The White Mouse" by the Gestapo because she was so hard to capture.

She is regarded as a heroine in France, which decorated her with its highest honour, the Legion d'Honneur, as well as three Croix de Guerre and a French Resistance Medal.

Ms Wake left Australia and moved to France in 1932, joining the Resistance after the German invasion in 1940 and helping shelter displaced Jews fleeing the Nazi regime.

She later recounted how she had first become aware of the cruelty of the Nazis during a visit to Austria in 1933.

"In Vienna they had a big wheel and they had the Jews tied to it, and the stormtroopers were there, whipping them. When we were going out of Vienna they took our photos. That was my experience of Hitler," she said.

Confirming Ms Wake's death today, New Zealand's veterans' affairs minister Judith Collins hailed her as a woman of exceptional courage and tenacity.

Family friend Les Partell said Ms Wake was one of the world's greatest women and had a knack for survival.

"Anyone else would have got knocked off left, right and centre," he said.

"She was just so good at what she did. She survived. She more than survived, she personified survival. I couldn't imagine her dying anyway, I just couldn't, and I am so surprised."

Credited with helping to save thousands of lives, Ms Wake was placed at the top of the Gestapo's most wanted list and fled France for England on the advice of her husband Henri Fiocca in 1943.

"Henri said, 'You have to leave', and I remember going out the door saying I'd do some shopping, that I'd be back soon. And I left and I never saw him again."

Trained as a spy by Britain's Special Operations Executive, she then returned to Nazi-occupied France to work with the Resistance in preparation for the D-Day landings in Normandy in June 1944.

Parachuted back into France, Ms Wake's job was to distribute weapons among Resistance fighters hiding in the mountains.

"In those days it was safer, or a woman had more chance than a man, to get around, because the Germans were taking men out just like that."

To arrange the delivery of weapons and other supplies, messages had to be sent via radio phones.

Ms Wake's group lost theirs during a raid by German troops.

This disastrous loss meant Ms Wake had to pedal more than 200km to another radio operator.

"The blokes didn't think I'd ever get back. I only volunteered for it not because I'm brave but because I was the only one who could do it, being a woman.

"I got back and they said "How are you?" I cried. I couldn't stand up, I couldn't sit down. I couldn't do anything. I just cried."

As well as the Legion d'Honneur, Ms Wake was awarded Britain's George Medal and the US Medal of Freedom.

But despite the international recognition, it took 60 years for Australia to honour her service, awarding her the Companion of the Order of Australia in 2004.

It is believed Ms Wake's health had recently deteriorated and she was admitted to the Kingston Hospital two weeks ago with a chest infection.

She had lived in London since 2001.

In accordance with her wishes, she will be cremated privately and her ashes scattered at Montlucon in central France next spring.

ABC/AAP