The contest is run by the Australian Mathematics Trust of the University of Canberra. Hong Kong has been taking part since 2001.
Last year, there were 8,000 contestants from the city including Andy Loo and Harry Yu Hoi-wai.
Andy, a fifth former at St Paul's Co-educational College, was one of the four medallists. At 16, he has represented Hong Kong nine times in international mathematics and physics competitions.
"I didn't use to think I was good at maths. In kindergarten, my teachers asked me what was five plus six, and I answered 10. I only have 10 fingers to count," Andy says. "In Primary Four, I read a book about maths and it fascinated me. I took interest in questions which use real life scenarios. I realised that maths is not about numbers, it is about thinking skills.
"Everything in this world has to do with maths. Numbers and space, the two basic concepts, are the universe's foundational elements."
Andy even believes pure mathematics, which has no application in real life, is of great value. "We may not see its value now. Like in the case of prime numbers, it was only after years that people used prime numbers to break secret codes. Maths is a form of human civilisation."
For 11-year-old Harry, it was a challenge to enter the Grade 7 competition and he obtained a perfect score. There were six perfect scores at the primary level and only one from Hong Kong.
"I didn't expect to do so well. The questions were difficult and I had to think hard to solve them," says the La Salle Primary School sixth grader.
Harry says he likes to read all the time. "My parents have to stop me sometimes."
His parents noticed their son's curiosity early on. "He likes to ask questions about things," says his accountant father. "We wanted him to be exposed to different subjects so we bought different books. Obviously, he chose maths."
"I like maths because it's useful," Harry says. "When I walk into a room and see the paint on the wall, I wonder how the shade is made by the right percentage of different colours. That's maths.
"I like to think. I don't like questions with a direct answer but the ones with different solutions. It's interesting to see how many solutions there are for one thing."
Like Andy, Harry has also won many competitions.
All the winners will be invited to join the High Achievers Club at the Polytechnic University and take part in its gifted and talented mathematics programme.
The Australian trust has appointed Polytechnic to run the contest from this year.
"Hong Kong students are performing exceptionally well in the AMC. [As partners] with Polytechnic, we will strive to develop the skills of [students] to be effective in problem solving in everyday life," says Professor Peter Taylor, executive director of the trust.