Two New Zealand women, who have fought for better access weight loss surgery, will this morning fly to Korea for surgery despite warnings from doctors that the flights could kill them.

Lynda Sim, aged 44, and Jasmin Sciascia, aged 25, were denied bariatric surgery - which reduces the stomach's size - in New Zealand because they lived in a District Health Board (DHB) area which did not fund the surgery.

In December last year the South Korean Government approached both women, offering to pay for them to have the weight loss surgery in South Korea.

The women who are morbidly obese - Ms Sciascia weighs about 200kg and Mrs Sim about 160kg - decided to take up the offer despite warnings from doctors that the flights over there could pose a health risk, and are due to go under the knife in Soochunhyang University Hospital in Seoul on Wednesday.

Ms Sciascia told the Dominion Post she was both "excited" and "terrified" about getting the operation.

Whanganui surgeon Clive Solomon, who had advocated for both woman to receive the surgery in New Zealand, said it was "bloody madness" that the woman were flying to Korea for the operations.

The women risked dying either on the operating table or on the flight over, he said.

Ms Sim said she was aware of the risks but was going ahead so she could have a better quality of life and a "healthy future".