Sonny Bill Williams stretches ahead of a match between New Zealand and South Africa on July 26 in Wellington. Photo: IC

All Blacks selectors backed star center Sonny Bill Williams to help achieve an unprecedented World Cup treble in Japan but dumped veteran prop Owen Franks from their 31-man squad on Wednesday.

The axing of 108-Test stalwart Franks was the major surprise, although the defending champions also had no room for rampaging midfielder Ngani Laumape or rejuvenated flanker Liam Squire.

They did, however, keep faith with struggling back Ben Smith as the New Zealanders target a third straight World Cup title and fourth overall.

Williams is among a trio of players hoping to secure a personal treble in Japan, alongside captain Kieran Read and lock Sam Whitelock.

Another nine members of the squad tasted success at the last rugby showpiece in Britain four years ago, while 19 are World Cup debutants.

The squad collectively boasts 1,195 Test caps and has eight players aged 30-plus.

Coach Steve Hansen said winning three titles in a row was "an awesome challenge."

"We know it's going to be hard, we know it's going to be tough... We're looking forward to taking that pressure head-on," he said.

Williams, the oldest member of the squad at 34, defied his doubters after an injury-plagued season to play a key role in this month's 36-0 victory over the Wallabies in Auckland.

He is now studying for a coaching certificate and another world crown might be enough to persuade him to call time on a remarkable career that also includes two rugby league NRL titles and victory in seven heavyweight boxing bouts.

'Most fiercely contested' Cup 

Hansen said two-time World Cup winner Franks had fallen victim to changes in the game, with the likes of Atu Moli and Angus Ta'avao offering more versatility.

"We believe the game requires us to have big, mobile number ones and threes [props]," he said.

Hookers Dane Coles, Codie Taylor and Liam Coltman were always regarded as certainties, with Coles probably edging Taylor as preferred starter.

Brodie Retallick returns from a shoulder injury to partner Whitelock in the locks, backed up by Patrick Tuipulotu and Scott Barrett, who can also play in the back row.

Read, Ardie Savea, Matt Todd and Luke ­Jacobson make up the rest of the loose forwards, with Squire's bid for late inclusion falling flat.

The highly rated Highlander only made himself available this week after voluntarily sitting out the recent Rugby Championship to deal with fitness and personal issues.

Anton Lienert-Brown, Jack Goodhue and fellow veteran Ryan Crotty join Williams in the centers, leaving Laumape on the outer.

As expected, Hansen is persisting with his new tactic of using two playmakers - Richie Mo'unga at fly-half and Beauden Barrett at fullback - to counter opponents' rush defense.

An excellent Super Rugby season sees Brad Weber join TJ Perenara and Aaron Smith in the three halfbacks selected by Hansen.

Rieko Ioane, Sevu Reece and George Bridge ensure the defending champions have potency on both wings, along with the versatile Jordie Barrett.  

Ben Smith remains in the mix, although recent poor form and Hansen's tactical switch mean he is more likely to feature on the wing than at fullback.

Hansen acknowledged the All Blacks' rivals had closed the gap on his team but warned the weight of ­expectation could be overwhelming for those not used to facing it. 

"This World Cup looks like it's ­going to be the most fiercely contested yet, with a number of teams thinking that they're going to win it," he said. "This is where I think we have a small ­advantage - we live here all the time." 

The All Blacks begin their World Cup defense with a blockbuster clash against South Africa on September 21, seeking to dominate a group that also includes Italy, Namibia and Canada.
Newspaper headline: ‘Awesome challenge’