Reports in New Zealand have suggested that Wellington's annual Sevens tournament, the third on the IRB Sevens World Series, is set to become even bigger with plans for a week-long festival.

Wellington City Council has unveiled plans to transform the successful event into a seven-day carnival within four years, but will stagger the transition.

An economic impact report into this year's tournament found the giant two-day party generated NZ$15.6 million in extra spending and drew 24,400 visitors to Wellington, including 10,000 who had no tickets.

The council plans to beef up events next year - the 10th anniversary of the Wellington Sevens - with a four-day line up to coincide with the Waitangi Day long weekend.

It will showcase waterfront concerts, festivals and parades, plus a two-night Courtenay Place street party with live music and big screens.

Planned events include a round-the-world yacht race visit, featuring 16 boats at Queens Wharf.

Officials hope the festival will help to generate $20 million in new spending and the council plans to extend the programme by one day each year, culminating in a week-long party by 2012.

Council events manager John Dawson said the number of people visiting Wellington for the Sevens was increasing, particularly from Auckland, and their spending had nearly doubled since 2001.

"People are spending longer in the city and while they're here they're spending more," he said.

"There is now a significant number of people who come to the sevens who do not have tickets, so they're coming to the city to take part in the experience."

Wellington Mayor Kerry Prendergast said $15.6 million generated from a two-day event was "phenomenal". It would be a mistake to introduce a seven-day tournament festival immediately as it "could fall flat".

She stressed that the council was not planning a week-long "drunken party" but a variety of events to keep tourist in the city.