All Blacks legend Jonah Lomu has named Ireland as the dark horse at this year's Rugby World Cup in New Zealand and warned any title contenders will underestimate Pacific teams at their peril.

While making it clear that he believes New Zealand are the favourites for the September 9 to October 23 tournament, Lomu said Ireland's ageing squad was not being given the respect it deserved.

"If there's a team that you have to be wary about, and not many people are talking about them, it's Ireland," Lomu told reporters in the Cook Islands during a trip to promote the World Cup.

"Purely because I've watched a lot of their teams. I've watched Leinster play in the Heineken Cup and they were very impressive, especially up front.

"A lot of those players are coming to the end of their career and they'll put everything on the line."

Ireland are fourth in the International Rugby Board (IRB) world rankings, the highest-placed northern hemisphere team, and showed their capability with a comprehensive 24-8 win over England in the Six Nations tournament.

Lomu, who has scored a record 15 tries at World Cups, said conditions in New Zealand would also suit the Irish, while veterans such as Brian O'Driscoll and Ronan O'Gara would be desperate to finish their last World Cup on a high.

The 36-year-old said Ireland's low profile could work to their advantage with the spotlight on "the usual suspects" such as South Africa, New Zealand and more recently Australia, after the Queensland Reds won the Super Rugby title.

Lomu, a devastating winger who made his international debut aged 19 but was forced into early retirement after a long battle with a rare kidney disease, said Pacific nations could play a crucial role in the tournament.

He said the hard-tackling islanders could destroy the chances of any side that did not take them seriously.

"The wild cards will be the Polynesians. If you take any of those Polynesian teams too lightly -- Fiji, Tonga, Samoa -- you could get punished physically, and that could take a toll on you later in the tournament," he said.

"To win the tournament, you've got to get through fresh but also without any injuries, cross your fingers that you don't have injuries to key players and be ready for the final."

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