The non-stop flight, NZ2 landed in Los Angeles on July 4, after leaving Auckland.
A coroner was called and normal processes were followed, a spokeswoman said.
She was not sure how long into the over 12 hour flight the death occurred.
Sergeant Karla Ortiz from Los Angeles International Airport police said the woman who died was aged in her 50s.
It was not known if she was a New Zealander.
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"There was CPR conducted and around 3 o'clock, LA time, [the airline] requested the Coroner and the Los Angles Police Department to respond."
Civil Aviation Authority spokesman Mike Richards said overseas authorities would be involved in the incident considering it happened offshore.