Kane Williamson reflected on a "special moment" but insists New Zealand will continue to work hard to improve after reaching the summit of the Test world rankings.

The Black Caps wrapped up victory over Pakistan by an innings and 176 runs on day four at Hagley Oval on Wednesday to seal a 2-0 series win and become the top-ranked Test nation for the first time.

Kyle Jamieson took 6-48 and had 11 wickets in the game to take the Man of the Match award as Pakistan were bowled out for 186 in their second innings.

New Zealand have now won six straight Tests for the first time and swept three consecutive home series', but captain Williamson still wants to see his side kick on.

"It's hard to beat really, I don't know how the rankings work exactly I know they span over a period of time, to achieve that standing means there's been a lot of hard work over a lot of matches, and trainings and all these sort of things to reach that, so it's very special moment from the guys," he said. 

"It's hard to talk about until the Test summer was over, so it's nice to sit back and perhaps take a moment and enjoy the moment.

"I sort of mentioned before in the after match [presentation] that the game is truly a game of small margins. 

"As a side we're pleased with the efforts that went into these last two games but we know the quality side Pakistan have and there were definitely moments in both games that went our way or perhaps moments that we seized and went a long way to putting the result in our favour. 

"It's a game of small margins, guys respect that and it's about working harder and harder to move forward as a collective. 

"We know our next matches will be overseas tours, and just constant adjustments, tinkering to try and perform well in those matches."

For Jamieson, it has been a superb start to Test cricket and he now has four five-fors in six Tests.

"He's a special talent but his attitude, the way he's come in and try to add to the group on or off the field is the most impressive thing. In many ways he's leading and that's great," Williamson added.

"Cricket is an interesting game and something Kyle is extremely good at with bat and ball, a very, very special talent. 

"I think if he continues to, and I'm sure he will he's got great head on his shoulders, bring that great attitude he has - things have come very thick and fast for Kyle and that's a really enjoyable part to the game, something he's learning about and learning about himself.

"But he has a strong desire to improve and pick the brains of the senior guys who have been around a long time. He's a humble guy who wants to get better, I've no doubt he will."