A baby girl has been born 14 weeks early in a rescue helicopter en route to Auckland Hospital.

Waiheke Island resident Ngaire Curran went into labour just before 9am on Saturday, just 26 weeks into her pregnancy.

Ms Curran gave birth to baby Charlie about 9.40am, as she lay on a stretcher in the rear of the helicopter, as she was being airlifted to hospital.

Westpac Helicopter paramedic Russell Clarke says there wasn't much space and he was forced to deliver the baby from the side.

"The baby came out very quickly with not much warning," he told APNZ.

"She was small enough to fit in my two hands."

It was the first time Mr Clarke had assisted a birth mid-flight.

Baby Charlie was born as the helicopter was above Bean Rock Lighthouse, off the coast of Mission Bay.

She was in a stable condition in Auckland Hospital's intensive care unit on Saturday night, while Ms Curran was in a hospital ward.

Charlie is Ms Curran's sixth child.