United Airlines has resumed its seasonal service between San Francisco and Auckland with a new aircraft - and newly configured crew quarters - that will fly the route daily from the middle of next month.

The service is running six times a week until December 17 before the boost to daily and the airline has introduced a new Boeing 777-300ER which has a big emphasis on its premium cabin which has its United Polaris product on board.

United's director of Australia and New Zealand sales, Julie Reid, said demand for the 60 business class seats was not just from corporate travellers but high-end leisure flyers as well.

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Come aboard United 777-300 and witness the rest areas for their crew.

The large number of business class seats is seen as a challenge to sell but she said bookings so far had been encouraging.

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"This aircraft has more capacity than what we had last year and so far we're very happy with bookings to date."

The Polaris business class is the airline's most significant product transformation in more than a decade and is part of a shift by the United States carriers to upgrade their aircraft after years of lagging behind other airlines.

United says it put more than 12,000 hours of research into Polaris with sleep emerging as the single most important priority for international business class travellers.

The design and sleep-enhancing features after feedback from hundreds of customers and staff, in-flight product simulations and more than 100 product evaluations.

The cabin has textured and softer touch materials that absorb aircraft noise and other sound within the cabin.

The seats were custom-designed by Acumen Design Associates and PriestmanGood and manufactured by Zodiac Seats in Britain.

Watch: United Airlines show off 777-300 in Auckland

Crew also have flash new quarters for long-haul flights. The pilot rest has two seats and two beds while flight attendants can relax in six small sleeping compartments that have narrow mattresses and privacy screens.

Use of the new aircraft on the New Zealand route comes as the airline retires the last of its Boeing 747s. United started flying the jumbo in 1970 and the last of the "Queen of the Skies" in the airline's fleet made its final flight between San Francisco and Honolulu on Wednesday.

United has a joint venture with Air New Zealand and is expanding in this region which an analyst says complicates the relationship.

United plans to fly between Houston and Sydney non-stop using a 787-9, which CAPA Centre for Aviation says in a report will increase its capacity in Australia by 26 per cent.

For Air New Zealand, United's growth into Australia complicates the pair's JV.

The JV excludes Australia, but Australia-US is an important transfer market for Air New Zealand, so part of Air New Zealand's business is undermined by greater US-Australia non-stop links," the report says.