(Reuters) -Kane Williamson hit an unbeaten century as New Zealand chased down a victory target of 267 to beat South Africa by seven wickets on the fourth day of the second test on Friday and clinch a first ever series win over the Proteas.

South Africa, severely depleted with most of their top players back home playing the SA20 tournament, battled hard to even up the series at 1-1 but were unable to make sufficient inroads into the home batting order.

Williamson's patient 133, his 32nd test century, was the mainstay of the Black Caps innings and a partnership of 152 with Will Young (60 not out) got them over the line in what was a record fourth-innings run chase in a test at Seddon Park.

The 2-0 series triumph will come with a hefty asterisk due to the inexperience of the South African squad and Neil Brand's tourists will take great credit for taking the contest down to the wire after losing the first test by a thumping 281 runs.

The hosts resumed on Friday on 40-1 with the match very much in the balance after Devon Conway had been dismissed by spinner Dane Piedt in the final over of play on day three.

Conway's fellow opener Tom Latham added nine runs to his overnight tally before he departed for 30, caught by Zubayr Hamza off Piedt, but that just brought Williamson to the crease to join Rachin Ravindra.