Last Saturday rival carrier American Airlines started its daily services between Auckland and Los Angeles. Air New Zealand has also expanded its operations into the United States, launching services to Houston last year. Fiji Airways had also started services to San Francisco via Nadi.
Auckland Airport chief executive Adrian Littlewood said despite the capacity increases it is estimated the US market is 30 per cent underserved.
Up to 30 million Americans were considering New Zealand as a destination for a holiday.
There was plenty of opportunity for the route to grow and expand in the future, said Littlewood.
United's senior vice president of worldwide sales, Dave Hilfman said his airline had carefully considered the size of the market.
"We believe we have the right capacity - that's the beauty of this joint venture," he said.
"We realise that competition makes everyone better - we have to pay close attention to that. ''
Ticket prices, product and advertising and marketing needed to be right to succeed in a competitive environment.
With anti-trust immunity United and Air New Zealand were able to share commercial strategies.
"When you have these joint ventures you get the opportunity to discuss price, scheduling - what keeps everyone on their toes is competition from many other good carriers. We need to stay very focussed on what they're doing and because of additional capacity brought in that makes us have to be competitive."
Hilfman said bookings so far had met expectations.
United last flew to Auckland in 2003 but pulled out of this country amid financial woes which hit the US airline industry hard following the 2001 terror attacks.
