Supercoach Wayne Bennett has backed the decision to allow Kalyn Ponga to change his international allegiance while declaring the Kangaroos should be nervous leading into this year's World Cup.

The International Rugby League announced on Wednesday night that the star fullback's request to switch his allegiance from Australia to New Zealand had been granted, clearing the path for the Ponga to play for the Kiwis later this year.

The shift means the 27-year-old could line up alongside Broncos star Reece Walsh for the Maroons during the State of Origin series before going head-to-head during the World Cup.

Bennett was on the coaching staff when New Zealand stunned Australia at the 2008 World Cup and said the fullback's switch is a boost for international rugby league.

"I'm certainly for it," Bennett said. "I've talked a lot about it before, it's the right thing to do and I think it's the way the game should be.

"It makes the international game stronger. Those players playing in Origin learn a lot.

"They get a lot out of it that they can take back to New Zealand and apply that there. That helps the other New Zealand players, so I'm very comfortable with it."

International rugby league is experiencing unprecedented growth on the back of the rise of the Pacific nations throughout the past decade.

A movement that started when Jason Taumalolo and Andrew Fifita shifted to Tonga in 2017 has rapidly gained pace and there are now five countries with genuine claims to win the World Cup.

Samoa stunned England to progress to the 2022 final and have been bolstered by Payne Haas' decision to play for the country.

The appetite for international rugby league has been seen in Australia and beyond, with the Kangaroos playing in front of record crowds during last year's Ashes tour of England.

Back home, New Zealand, Tonga and Samoa played out a gripping Pacific Championships in front of record crowds and staggering TV audiences.

The excitement sets the foundation for a gripping World Cup and Bennett is expecting a hotly-contested tournament.

"Who would have thought six years ago that Australia would be in England playing in an Ashes series and we'd have Samoa, Tonga and New Zealand here and every stadium they played in would be packed out," Bennett said.

"Every stadium in New Zealand and Australia sold out. No one would have predicted that four or five years ago so we've come a long way.

"If you're going into this year's World Cup and coaching Australia, it's not going to be a gift to them. If you think it's just going to happen, that they'll win, no they will have to win it. Anyone who wins the World Cup this year has earned it."

While excited for the World Cup at the end of the year, Bennett's immediate focus is on South Sydney's clash with the Roosters on Friday night.

The Rabbitohs enjoyed an impressive win over the Dolphins last week and are looking to back that performance up against their fierce rivals at Allianz Stadium.

A big crowd is expected as Alex Johnston chases the all-time NRL try-scoring record. The South Sydney winger enters the game one try behind Ken Irvine and will create history if he scores a double.

Bennett said the Papua New Guinea star is one of the best wingers he's seen in his five-decade association with the elite game and looks forward to celebrating the veteran's achievement once he eclipses Irvine.

"He's a different type of winger," Bennett said. "If you look closely, Ken Irvine is pretty similar to Alex. They're not big guys, they don't run over the top of people but they've got good skill and guile, great anticipation and a feel for the game.

"Some of the tries that Alex has scored, you'd put other wingers in that position and they wouldn't score those tries because they don't have the feel he has to come on to the ball at the right pace and get himself over in the corner."