Owen Franks was surprisingly left out of the All Blacks' 31-man Rugby World Cup squad on Wednesday.

Franks has made 108 Test appearances for New Zealand, but the 31-year-old was overlooked for the showpiece tournament beginning in Japan next month.

All Blacks head coach Steve Hansen said it was tough for the two-time defending champions to leave Franks out.

"He is one of the great All Blacks, he's played over 100 Tests, but unfortunately we believe the game requires us to have big mobile one and threes and in this case we think the other guys are more so," he told a news conference.

"It was a tough decision."

There was also no room in the squad for Ngani Laumape, who has scored eight tries in 13 matches for the All Blacks.

Kieran Read will again captain the All Blacks as he heads to his third World Cup along with Sam Whitelock and Sonny Bill Williams.

Of the 31-man squad, 19 players are set for their first World Cup appearances.

"The All Blacks selectors would like to congratulate all those selected for Rugby World Cup 2019," Hansen said.

"It's a special moment being named in any All Blacks squad but especially when it's the Rugby World Cup and they and their families can be incredibly proud of what they've achieved.

"As always, we'd also like to take a moment to respect the effort and disappointment of those who've missed out. It's a tough time in anyone's career.

"The selectors wanted to point out that it wasn't a case of anyone not being good enough to be selected, but more the fact that we can only take 31, so there was always going to be some very talented athletes that would miss out.

"Having said that, as we know from previous Rugby World Cups and other campaigns, we may have injuries so those players who missed out may get an opportunity."

The All Blacks will open their Pool B campaign against South Africa on September 21 before facing Canada, Namibia and Italy.

New Zealand's 31-man Rugby World Cup squad in full:

Forwards: Scott Barrett, Sam Cane, Dane Coles, Liam Coltman, Luke Jacobson, Nepo Laulala, Joe Moody, Atu Moli, Kieran Read, Brodie Retallick, Ardie Savea, Angus Ta'avao, Codie Taylor, Matt Todd, Patrick Tuipulotu, Ofa Tuungafasi, Samuel Whitelock.

Backs: Beauden Barrett, Jordie Barrett, George Bridge, Ryan Crotty, Jack Goodhue, Rieko Ioane, Anton Lienert-Brown, Richie Mo'unga, TJ Perenara, Sevu Reece, Aaron Smith, Ben Smith, Brad Weber, Sonny Bill Williams.