The flight time will be Air New Zealand's longest at 15 hours northbound and just over 16 hours coming home.

The advantage for travellers is that Chicago's O'Hare airport operates as United Airlines' hub with more flights out of Chicago than any other airline to around 100 destinations across North America.

As part of the announcement, fellow Star Alliance airline United will make its service between Auckland and San Francisco year-round rather than seasonal.

Flights to Chicago on Air New Zealand and United's expanded Auckland-San Francisco service are on sale today.

Newshub.