New Zealand won their third successive junior world rugby title with a sublime seven-try 62-17 win over an outclassed Australia in Rosario, Argentina, today (NZT).

Coach Dave Rennie named the same 15 who started in their 36-7 semifinal win over South Africa which followed decisive pool victories over Fiji, Samoa and Wales.

The cohesion, composure and confidence from those wins was immediately obvious as hooker Liam Coltman crossed for the New Zealanders' first try barely 30 seconds after kickoff.

Although the Australians replied five minutes later with a Matt Toomua penalty, that was the sole extent of their scoring until fullback Luke Morahan crossed in the 55th minute.

In contrast, the New Zealanders dominated possession and territory, controlling the game with an impressive scrum and running with pace and precision.

Fullback Tom Marshall and wing Telusa Veainu also crossed in the first half, and with New Zealand captain Tyler Bleyendaal in superb form directing play from first five-eighth, they went into the halftime break 25-3 ahead.

The misery continued for Australia in the second spell with flanker Sean Polwart crashing over for New Zealand's fourth try barely four minutes after the restart.

Bleyendaal capped off a brilliant tournament with a try after Julian Savea - who finished the tournament with eight tries - rampaged down the wing, turned the Australian defence inside out and then off-loaded for his captain to score.

A yellow card for Coltman in the 63rd minute eased the pressure on Australia, and they were able to add to Morahan's five-pointer in the 71st minute when wing Kamami Sitauti showed his sevens skills to cross for a consolation try.

The New Zealanders finished strongly, Veainu crossing for two more tries to notch a hat-trick and New Zealand's 100th try in junior world championship rugby.

It was Australia's first-ever final after they beat England 28-16 in the semifinal.

New Zealand 62 (Telusa Veainu 3, Liam Coltman, Tom Marshall, Sean Polwart, Tyler Bleyendaal tries; Tyler Bleyendaal 4 con, 5 pen; Hayden Parker 2 con) Australia 17 (Luke Morahan, Kimami Sitauti tries; Matt Toomua 2 con, pen). Halftime: 25-3.