To moved to Sydney from Hong Kong when he was two years old, and won silver as part of the 400-metre medley relay squad at the 2013 World Championships in Barcelona.
He also claimed six medals at the 2010 Youth Olympics in Singapore and in 2009 broke Ian Thorpe’s decade-old Australian record in the 200m individual medley.
According to news.com.au, To was currently training to compete at next years Olympic Games in Tokyo as part of the Hong Kong swim team.
A Hong Kong sports institute spokesperson has released the following statement: “(To) felt unwell at a training session and was taken to hospital where sadly, he passed away.
“Kenneth was known as a truly exceptional person, warm, funny and kind.”
Australian swimming legend and Olympic medalist James Magnussen paid tribute to Kenneth on his Instagram account, posting a photo of himself on the swimming blocks alongside To.
"Shocking news to hear of the passing of my competitor but most of all, friend - @kennethkhto,", James wrote, "We've been racing each other and making teams together since we were 16.
"He will remain one of the fiercest competitors I've ever stood on the blocks next to. I firmly believe that for a long period he was pound for pound, the best swimmer in the world.
"RIP little guy, you won't be forgotten."
The Australian swimming team also expressed their shock and sympathies, posting a photo of To on Twitter with the following statement: "The Dolphins are extremely saddened by the sudden passing of our friend and teammate Kenneth To. We send his family and friends strength at this incredibly difficult time."
Our thoughts are with Kenneth To and his family.
More to come as this story develops.