Virgin Australia will add more seats across the Tasman over summer as its alliance with Air New Zealand ends.

Virgin 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 had already announced a 13 per cent increase in capacity from October 28 but today said it would add thousands more seats as part of a regional expansion later this year.

It will add more than 65 return services to its international short haul network.

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It has added 18 return services between Sydney and Queenstown in addition to existing Monday-Friday services during this period.

It also added 18 return weekend services between Melbourne and Queenstown, in addition to the previously announced Monday, Wednesday and Friday services during
this period.

Virgin also added nine return services between Brisbane and Christchurch during the Christmas/New Year period.

The airline will also fly more from Australia to Samoa and Vanuatu over summer.

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

The airline will be the only carrier offering Business Class on the Melbourne-Queenstown route, which has been welcomed by travel agents.

Virgin has more than 70 of the single aisle 737-800s and has said it could juggle existing aircraft to provide extra seats across the Tasman.

Earlier this year Air New Zealand announced it too was increasing transtasman capacity after pulling the pin on a seven-year deal with Virgin from October 28.

Air New Zealand will launch two new routes across the Tasman from December and will 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, they will compete hard against each other afterwards.