Air New Zealand had dropped its standard economy fares with $30 to $100 off one-way tickets, and $250 to $400 off one-way business class travel, depending on the time of the year. The new fares take effect on or after March 15.
There would be extra savings with sale fares.
"We'd expect ... with Hawaiian coming in we'll see more promotional fares popping up and past history has shown that's very competitive."
An Air New Zealand spokeswoman said the airline aimed to be competitive in all the markets it operates.
"Hawaii is a very popular destination for Air New Zealand customers and a key route which we have a long history of serving."
Following Hawaiian's announcement it was starting flights, Air New Zealand said it would add capacity with a third weekly service and the addition of a bigger aircraft during June to September.
Hawaiian has decided to put on a bigger aircraft in response to strong early demand.
Thomas said strong bookings did not appear to be at the expense of other island destinations.
Bookings for next year, particularly to North America, had been strong and had been helped by the strength of the New Zealand dollar.