Spencer's triumph helped the US top the team standings as they edged Hawaii with a total of 7,003 points, 263 in front of their nearest rivals.

Hosts Japan did enough for third place as they earned 6,286 points.

The four titles on offer at the event in Hyuga were all won by different countries as the US, Japan, Argentina and Hawaii all took home a gold medal.

Spencer powered to her maiden junior world crown with a score of 18.94 as she fought off competition from Keala Tomoda-Bannert of Hawaii and fellow American Samantha Sibley, who claimed silver and bronze respectively.

Gabriela Bryan of Hawaii took the copper medal.

"This has been my dream since I started surfing,” said Spencer. 

“I can’t believe it’s actually true - I’m speechless.

“I wanted the gold so bad and getting that nine right off the bat boosted my confidence so much. 

"After that I just needed another score to back it up.

 “I would be so honoured to represent the USA in the Tokyo 2020 Olympics, but I know it will take a lot of hard work because there are so many girls that rip."

Bryan's compatriot sealed her second ISA World Junior title as she won the girls' under-18 event after recording a score of 16.27 points.

Leilani McGonagle of Costa Rica took silver, Summer Macedo of Hawaii earned bronze and the copper medal went to American Kirra Pinkerton.

In the boys' events, Joh Azuchi and Ignacio Gundesen made history as the first ISA World Junior Championship gold medallists from Japan and Argentina respectively.

Azuchi secured victory in the under-16 competition as he scored 16.60 points.

Taro Watanabe of the US was forced to settle for silver, while Japan's Keanu Chris Kamiyama claimed bronze and Brazil’s Lucas Vicente the copper.

Gundesen topped the podium in the under-18 event on 15.27 points as he ousted American Noah Hill and Cody Young of Hawaii, who finished second and third.

Australia’s Dylan Moffat was the recipient of the copper medal.