Tonga's prime minister says this year's rugby world cup will not be a real competition because "unfair" eligibility rules prevent Pacific nations from fielding some of their best players.

Lord Tu'ivakano said International Rugby Board (IRB) rules barring a player who has represented one country from ever taking the field for another, protected the game's traditional powers from being challenged.

The law is a sore point for Pacific nations, whose best players are often lured to New Zealand or Australia as youngsters, but cannot represent their homeland even after their careers with their adopted countries are over.

"If they're going to have a real World Cup, then they need to give the other countries the chance to have their own players," he told AFP in an interview on Tuesday.

Tu'ivakano said Tonga had players in top international competitions who could not represent their country at the World Cup, which runs from September 9 to October 23 in New Zealand, robbing the team of valuable experience.

"Now we're just trying to find people who are playing regional in New Zealand," he said. "Now some of our boys don't have international experience."

Tu'ivakano said rugby league allowed players to switch nationalities but the IRB had proved inflexible in November when it rejected a New Zealand-sponsored move to relax eligibility rules.

"It's very unfair, I think they really need to look at it," he said.

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