Kane Williamson is still finding new and interesting ways to score runs, even if the rest of us are running out of superlatives to describe them.

This time he brought a couple of his mates along with him as New Zealand posted an enormous total to stand on the cusp of completing a four-from-four sweep of their test season.

At stumps on an electric day three, Pakistan are 8-1, trailing New Zealand by a massive 354 runs.

The 30-year-old Williamson added a second double-century to his preposterous summer CV that now reads 238, 21, 129 and the 251 he scored in his only bat against the West Indies.

If you're the counting type, that's 639 runs at an average of 160, a figure that would have been higher if he hadn't three times sacrificed his wicket in the search for quick runs.

He was extraordinary here in Christchurch, first pulling New Zealand through a difficult phase in partnership with Henry Nicholls, going on to his first century on this ground and then adding splashes of vivid colour as he surged to his fourth test double century, a figure matched only by the man who has just anointed him the best batsman in the world, Brendon McCullum.

The former New Zealand captain reason for elevating him above the likes of Virat Kohli and Steve Smith was that he isn't just on a search for constant improvement but that he drags his teammates along with him in that quest.

He couldn't have asked for a timelier Exhibit A.

Take Daryl Mitchell. Coming to the wicket at 452-5 can be a thankless task. All the hard work has been done and you're expected to arrive at the crease with your foot firmly on the accelerator.

The pair put on 133 in quick time without ever looking truly hurried. On a cold day under leaden skies, Pakistan were left enervated by Williamson's flicks, cuts and checked drives, and Mitchell's more pugnacious stroke play.

When Williamson was finally dismissed Mitchell continued, hurrying to a maiden test century of such quality that more look inevitable.

It is a measure of what drives this team that Williamson showed more joy from beyond the boundary in Mitchell's milestone than he did for any of his own.

While it seems a long time ago, Henry Nicholls carved himself out an unforgettable slice piece of the series that it feels cruel to relegate to the third-most significant knock of the day.

He returned to the crease on 89 on day three, only after a net session determined he could, only just, bat with a left calf strain.

He left having scored 157 and sharing a partnership worth 369 with Williamson, the highest for any wicket in a test between these two countries and the third all-time for New Zealand.

Nicholls' footwork and running between the wickets was restricted, his heart and class were not. Once he reached three figures it was clear he was out there for a good time not a long time, but some of the shot-making was exquisite, none more than the shuffle down the crease to flick a quick bowler over midwicket for six.

While Nicholls and Mitchell shared the nomination for best supporting actor, Williamson remained the leading light.

He became just the third New Zealander to score 7000 test runs. Only Stephen Fleming (7172) and Ross Taylor (7379) have scored more. He did it in fewer innings than all but 13 players in history before him.

His 24th century places him among the greats. There will be more to come.