McCullum hit 188-ball 202 while Williamson made 192 as New Zealand closed the third day at 637-8 with a world record of 19 sixes to pulversie a hapless Pakistan.
That gave New Zealand a mammoth lead of 286 runs over Pakistan’s first innings total of 351, setting them up strongly for a series-levelling win.
Pakistan lead the three-match series 1-0 after winning the first Test in Abu Dhabi by 248 runs and drawing the second in Dubai.
New Zealand surpassed Australia’s record of 17 sixes in a Test innings against Zimbabwe at Perth in 2003.
This also becomes the highest total by New Zealand against Pakistan, beating the 563 they made at Hobart in 2003.
Ross Taylor, Corey Anderson and Tim Southee all made 50 each to enjoy a dominating day for their team.
In the morning McCullum became one of only four batsmen to score three double-hundreds in a year.
The New Zealand skipper also created a new second-wicket record for New Zealand in all Test cricket of 297 with Williamson.
– Over the roof –
McCullum jumped out of his crease to hit Shah over the stadium roof at long-on for his 11th six to complete his double-hundred off just 186 deliveries.
This is his third double-hundred this year, following his two against India at home in February, making him the fourth batsmen to score three or more double-hundreds in a year.
Michael Clarke (four scores of over 200 in 2012) Ricky Ponting (three in 2003) and Don Bradman (three in 1930) — all from Australia — are the only other players to have achieved the feat.
It was an innings of full control which battered the Pakistani bowlers into submission, studded with 21 fours and 11 sixes — one short of the record of most sixes in an innings held by Pakistan’s Wasim Akram, against Zimbabwe in 1996.
McCullum was finally bowled by Shah, much to the relief of the Pakistan bowlers who were looking for wickets after New Zealand resumed the day on a strong 249-1.
The McCullum-Williamson stand bettered New Zealand’s all-time previous second-wicket stand of 241 held by Andrew Jones and John Wright against England at Wellington in 1992.
Willimson reached his hundred with a sweetly-timed on-drive to the boundary off paceman Mohammad Talha, completing his three-figures off 124 balls with 13 fours and a six.
Williamson hit 23 fours and a six off 243 deliveries and added another 116 for the third wicket with Taylor.
Williamson’s previous best of 161 not out was against the West Indies at Barbados in June this year.
He was finally caught in the slip off Rahat off the first ball after tea.
Both teams had to abandon the second day’s play on Thursday to mourn the tragic death of Australian batsman Phillip Hughes, who died after being hit by a bouncer during a match in Sydney.
The Test has been extended until Monday. -AFP