Left wing Digby Ioane claimed a hat trick of tries and created several others as Australia ran out comfortable 66-19 winners over a determined Japan in the Under 19 World Cup.

Australia now meet Wales in a play-off for fifth and sixth on Monday after the Dragons beat Scotland 29-16.

The Australians will be happy with the result, but not with their injury tally. Captain and number eight Julian Salvi failed to appear after halftime after sustaining a suspected shoulder injury early in the first half, while replacement centre Anton Lavin ended the match after suspected rupturing of tendons in his left knee.

Australia began their victory march in the third minute, when bulky centre Alexander Pedan barged his way through the pintsized defence from a lineout 30 metres out to score the first of his two tries.

The Australians duly took up residence on the Japanese 22, but on 20 minutes the underdogs capitalised on a scrappy moment among the Aussie backs and lock Taro Kenjo crashed over for the try.

It took Australia just three minutes to regain their composure with strong running and slick passing between Pedan, right wing Lloyd Jones and hooker Geoff Abram, with the latter claiming the touchdown.

A minute later Ioane blasted through the Japanese line to score his first try, and it was all but game over at 21-5.

Before the half was out Lloyd Johannsen found himself on the end of a line movement and scored, and Ioane grabbed his second on the halftime whistle courtesy of two consecutive tap-and-go penalties.

Replacement hooker Sean Fell made it 40-5 in the opening minute of the second half with a textbook example of how to score from the restart, but still the Japanese refused to accept their hiding.

Instead, they harried the attacking Australians, won possession from broken play and sent left wing Rikiya Asami wriggling through the defence to score their second try.

Ioane responded by smashing a hole in the Japanese defence to put Pedan away for his second.

The winger completed his hattrick in the 51st minute, zipping upfield effortlessly after Australia had won a lineout.

Three minutes after that Ioane did all the hard work that resulted in a try by replacement fullback Tajohn Malaita.

Lock Dylan Sigg earned Australia's last try from a close range tap penalty, but the last hurrah went to Japan when lock Masakazu Toyota emerged smiling from a tryline pile-up.

Australia - Tries: Alexander Pedan (2), Geoff Abram, Digby Ioane (3), Lloyd Johansson, Sean Fell, Tajohn Malaita, Dylan Sigg. Conversions: Julian Salvi, Scott Daruda (3), Johansson (2), Pedan (2). Japan - Tries: Taro Kenjo, Rikiya Asami, Masakazu Toyota. Conversions: Ayumu Goroumaru (2).