New Zealand reached their first ever Cricket World Cup final after securing a thrilling four-wicket Duckworth-Lewis victory over South Africa in the first semi-final in Auckland on Tuesday.

Faf du Plessis (82), AB de Villiers (65 not out) and 49 from 18 balls from David Miller helped South Africa amass 281 for five after a two-hour rain delay reduced the Eden Park encounter to 43 overs per side.

Brendon McCullum (59), Corey Anderson (58) and Grant Elliott (84 not out) kept New Zealand competitive in their chase of 298 runs and, needing 12 off the final over, Elliott hit Dale Steyn for six off the penultimate ball of the match to send the Black Caps into Sunday's final.

New Zealand will face either fellow co-hosts Australia or India in the tournament showpiece in Melbourne in five days' time.

South Africa went in to bat after winning the toss but were left ruing their decision after in-form seamer Trent Boult accounted for Hashim Amla (10) and Quinton de Kock (14) inside eight overs.

Du Plessis and Rilee Rossouw (39) shared 83 runs for the third wicket before the latter edged Anderson to backward point where Martin Guptill made a spectacular one-handed catch to depart for 39.

Kane Williamson put down a difficult chance to dismiss De Villiers on 38 and was punished as the captain hit the next three balls for a combined 14 runs to bring up his 50 off 32 balls.

De Villiers' and Du Plessis' century partnership was then brought up off 71 deliveries before rain forced the players off after 38 overs.

The teams returned after a two-hour interruption and Anderson had Du Plessis caught behind for 82 with just the second ball back.

Miller hit six fours and three sixes as he raced to 49 from 18 deliveries before also edging Anderson (three for 72) behind in the last over.

New Zealand made their customary speedy start with McCullum clubbing Steyn for a six in the first over before dispatching Vernon Philander for a six and two fours in the second.

The skipper brought New Zealand's fifty at the start of the fifth over with a ferociously-driven six that cleared the long off boundary with ease, before hooking the paceman for another maximum three balls later to bring up his half-century.

De Villiers' decision to bring Morne Morkel into the attack paid immediate dividends when McCullum mistimed to mid-on and Williamson dragged on to his stumps to give the 6ft 5in paceman two wickets in as many overs.

Guptill and Ross Taylor set about picking up where McCullum left off but the boundaries dried up and Guptill was run out for 34 attempting a single that was simply not there. Taylor departed shortly after for 30 when JP Duminy tricked him into edging behind.

New Zealand's hopes of victory now rested firmly on the shoulders of Elliott and Anderson and the pair kept the Black Caps in the match with half centuries in a fifth-wicket partnership of 103 runs in 16.2 overs.

Morkel (three for 59) was South Africa's hero once again when he removed Anderson, who top-edged to square leg, and New Zealand suffered a further blow moments later when middle-order danger man Luke Ronchi (eight) flicked tamely to mid-wicket.

At that point the Black Caps needed 29 runs from the final three overs and some subsequent boundary-saving fielding from South Africa meant 23 were required from the last two.

The Eden Park faithful held their breath when Elliott skied Morkel's final delivery but a collision between Duminy and Farhaan Behardien ensured the ball dropped safe and he and Daniel Vettori ran two.

That meant 12 runs were required off the final over from Steyn and, after Vettori hit the third ball to the ropes, Elliott launched the penultimate delivery for six to send New Zealand into their first ever World Cup final and cue wild celebrations across the country.