Virgin Australia has fired back in what is shaping up as a post-divorce battle with Air New Zealand across the Tasman, putting on more than 40,000 extra seats next summer.

The Australian airline says its transtasman capacity will increase 13 per cent, with 43,000 extra seats from October 28.

Virgin Australia will start up to five flights per week between Sydney and Wellington, as well as up to four flights per week between Melbourne and Queenstown.

Auckland-Sydney flights will increase to three times a day during the week and twice daily on weekends, Auckland-Melbourne is increased up to double daily every day and Auckland-Brisbane up to two services and up to three on peak days.

There will be a slight reduction on two other routes.

Frequency between Christchurch and Melbourne will drop from 11 flights per week to a daily service, and Brisbane-Wellington from up to 14 services per week to nine.

"As well as increasing frequency on key routes from Auckland, we have also improved the timing of some of our New Zealand flights to better suit the needs of both leisure and business travellers,'' said group executive Rob Sharp.

''Our entry into the Melbourne-Queenstown market will bring some much-needed competition to the premium leisure sector, with Virgin Australia the only airline to offer Business Class on this route.''

Transtasman travellers are set to win from more competition between the airlines. More seats usually lead to cheaper fares.

Last week Air New Zealand announced it too was increasing transtasman capacity after saying it would end a seven-year deal with Virgin from October 28. Air New Zealand will launch two new routes across the Tasman from December this year and add an extra 15 per cent seat capacity across all its Tasman services year-on-year.

It will operate up to four times a week between Queenstown and Brisbane, increasing the airline's total international capacity out of the resort town by 20 per cent. It will also operate up to five times a week between Wellington and Brisbane, a 15 per cent increase or 20,000 seats.

While the airlines are co-operating until the end of October, the gloves will be off afterwards.

When Air New Zealand delivered the news early this month to Virgin, its chief executive and managing director John Borghetti told the Herald: ''We were we thought with a good alliance partner and now we won't. When we're not we will compete very vigorously.''

Sean Berenson, Flight Centre NZ general manager product, said the extra capacity proved what a competitive route the Tasman was.

''At Flight Centre we welcome competition on popular routes; history shows its often good news for our customers in terms of affordability and accessibility,''

He said the addition of Business Class on the Melbourne-Queenstown route was exciting for customers.

Many travellers were now seeing that the offering in premium cabins was a viable and affordable option, particularly given that over peak seasons capacity ex New Zealand is often at its maximum.