Shaun Johnson turned on the style as co-hosts New Zealand put a turbulent Rugby League World Cup build-up behind them by hammering Samoa 38-8 in their opening Group B game at Mount Smart Stadium.

Kiwis coach David Kidwell was jolted when superstar Jason Taumalolo was among several players who defected to Tonga soon before the tournament got under way, while Jesse Bromwich and Kevin Proctor were overlooked following a drugs scandal.

New Zealand showed their strength in depth in Auckland on Saturday, though, outscoring Samoa by seven tries to two in a clinical performance, although the sight of Gerard Beale being carted off with what appeared to be a serious injury was another blow for Kidwell.

Johnson pulled the strings, scoring a first-half try, slotting five conversions and also turning provider in an influential display from the half-back, who will have a major part to play if New Zealand can go one better than finishing runner-up to Australia, as they did in England four years ago.

Jordan Rapana opened the scoring with an early try, but Ken Maumalo gave Samoa hope with a score just before half-time after Johnson went over.

The Kiwis ran away with it in the second half, Brad Takairangi, Nelson Asofa-Solomona and Isaac Liu scoring debut tries, with Kodi Nikorima and Roger Tuivasa-Sheck also crossing before Joseph Paulo rounded off the scoring for Samoa right at the end.

The clinical Rapana put the Kiwis in front only three minutes in after exchanging passes with the lively Johnson, whose conversion attempt struck the post.

Samoa responded with vigour, imposing huge pressure on a Kiwis defence which stood firm and Johnson took advantage of some slack defending at the other end to go under the posts for a try which he converted following slick handling from Simon Mannering and Thomas Leuluai.

Maumalo reduced the deficit to 10-4 three minutes before the break by stepping inside to finish off a slick move on the left, but the winger undid that good work by spilling the ball under pressure from Joseph Tapine in the in-goal area to gift Takairangi a four-pointer early in the second half.

Nikorima showed a sharp turn of foot to dive over for a fourth New Zealand try, Johnson providing the assist with a perfectly weighted no-look kick, and Liu came off the bench to add another try three minutes later.

The Kiwis suffered a blow when Beale was carted off following lengthy treatment to a suspected broken leg, before Tuivasa-Sheck took a pass from Nikorima to race away for a sixth New Zealand try and the excellent Asofa-Solomona claimed a deserved debut try before Paulo crossed at the death. 

Captain David Mead earlier made history by scoring Papua New Guinea's first World Cup hat-trick in a 10-try 50-6 demolition of Wales in Group C.