Air New Zealand's flight from New York to Auckland will have to touch down in Nadi for a fuel stop because of strong headwinds in the latest setback for the operation.

The NZ1 flight, launched as a non-stop operation last month, will do a "gas and go" stop in Fiji tomorrow.

Air New Zealand chief operating officer Alex Marren said due to a combination of strong headwinds caused by jetstreams and turbulence across the United States resulting in a longer flight time, the aircraft will make a short stop to refuel.

"Our priority is getting customers to where they need to go safely. It'll mean a short stop in Nadi to refuel and swap over crew, which means NZ1 will arrive into Auckland around 5 hours later than expected."

All 180 customers were advised prior to departure and the airline was working to rebook any onward travel.

"We want to thank our customers for their patience and understanding with the changes to their travel plans."

There are crew heading up to Nadi on today's scheduled service to be ready to operate the flight from Nadi to Auckland tomorrow.

Air NZ's longest route has hit headwinds since it launched. Photo / Supplied

Airlines plan for a refuelling stop when there is adverse weather and Nadi has also been used in previous years for other routes on our network.

"While we can't control the weather, we can plan for it and using our standard contingency plan to refuel means we get our customers safely to their destination," Marren said.

The westbound flight has hit persistently strong winds since launching early in September. About 60 passengers' bags had to be offloaded before its first flight from JFK Airport to Auckland and it has been plagued by strong jetstream winds on several days since. Some passengers were paid to fly indirectly to New Zealand before one flight.

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Air New Zealand's new Dreamliners on order will be fitted out and equipped to better handle the 14,200km flight, now the fourth longest in the world.

In the months leading up to the service the airline outlined how a stop-off in Nadi would be a possibility.

In the lead-up to the flight, the Herald reported that pilots face vast tunnels of wind, jetstreams that blow at up to 400km/h in the upper troposphere, formed when cold and hot air meet. Blowing from west to east, jet streams hundreds of kilometres wide snake around the planet for thousands of kilometres and will influence the route's commercial viability.

The airline analysed more than 10 years of weather data in the lead-up to the flight to help establish the operational and commercial viability of the route.

The jetstreams are largely invisible and blow hardest in winter when the temperature difference between cold and warm air is at its greatest. Aircraft which fly through them face turbulence described by one pilot as being like those dull staccato bumps experienced on flights from the United States as they approach New Zealand. In some cases, flights can be routed around them.