Tokyo - New Zealand assistant coach Ian Foster has promised to show Canada and Namibia little mercy in their next Rugby World Cup fixtures as the All Blacks head off to a hot spring resort.

The defending champions move to picturesque Beppu in southern Japan on Tuesday to begin eight days of training before they take on Canada in Oita.

But Foster insisted on Monday that New Zealand, who overpowered the Springboks 23-13 in their Pool B opener, would not be there for the expensive spa treatments.

"I'm assuming people think we might (switch off) and that's the danger of it," he told reporters.

"But the reality is we have got three more opportunities to hone our game and get it to the point we need it to be at," warned Foster, ominously for Italy who face the All Blacks in their final group match.

"The minute we think we've had one good game and we've made it, we're going to get smacked," he added.

"Certainly there will be no loosening of the reins."

Worryingly for their rivals, the treble-chasing All Blacks were below their rampaging best against South Africa but still had too much for the Boks, one of several teams who were tipped to challenge New Zealand in Japan.

"We were delighted with the win but it was far from perfect and we all know that," admitted Foster.

"There's still plenty of work to do, but when the intention is there, and the desire to play rugby, then we've got to gamble that we're going to get more right than wrong," he added.

"We put ourselves under a lot of pressure in that game because it was obviously a big one for the pool. But we loved having that massive game early because it gives us a clear picture of where we're at."

Foster noted the All Blacks had "a lot of battered and bruised" players but offered a glimmer of hope that influential lock Brodie Retallick could return from his shoulder injury to play some part in the pool games.

"He's progressing ahead of schedule and going really good," said Foster. "He's a world-class lock and he's very important to us."

New Zealand's victory over South Africa puts them on course to face the runners-up of Pool A, which is likely to be Scotland or hosts Japan after Ireland smashed the Scots 27-3 at the weekend in what Foster described as a "very ruthless performance."

Meanwhile, Anton Lienert-Brown provided some levity before the All Blacks leave for the southern island of Kyushu when asked if he had bought a birthday gift for fellow centre Ryan Crotty, who turned 31 on Monday.

"He told me he was 25!" he joked.

"I might give him a cuddle."

Lienert-Brown also poked fun at Scott Barrett's try-scoring dive against South Africa, calling it "terrible, an old man's dive."

But on a serious note, he insisted the All Blacks would be at full throttle against Canada, Namibia and Italy.

"It doesn't matter what team we play, we always turn up," said Lienert-Brown.

"That's what the black jersey demands of us. We expect ourselves to turn up and if we don't it will be a tough day at the office."