People watching a DJ perform at a popular Sydney nightclub were horrified when the man suddenly collapsed in the middle of his set.

Alf Nguyen gave no indication he wasn't feeling well in the moments before he went into cardiac arrest while performing at the Tokyo Sing Song club at the Marlborough Hotel in Newtown on July 13, reports news.com.au.

There were attempts to resuscitate the 42-year-old but he could not be saved.

An autopsy revealed Mr Nguyen had advanced coronary heart disease and had likely lived with the condition for several years.

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In some cases of heart disease there can be very few symptoms, often making it a silent killer.

Mr Nguyen's sudden passing has left his family and friends completely devastated.

A GoFundMe page has been set up by the couple's friend, Zee Moo, to support his wife Rita and five-year-old son Chauncy, who was recently diagnosed with autism.

The money raised will go towards funeral costs, bills, living expenses and care for the couple's son.

So far the page has raised over $47,000.

Ms Moo described Mr Nguyen as having an "enormous love of life" and "never-ending love for family".

"His unwavering loyalty to friends was legendary, as was his passion for music, basketball, and amazing — if sometimes bizarre — old-school Asian eats," she wrote on the fundraising page.

"Alf Nguyen, aka A.L.F/First Grandson, was a legend in the Sydney music scene, admired and loved by his musical comrades and all those he entertained with his music.

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He was always wearing a smile, ever happy to see mates, and always ready with a warm embrace for those he hadn't seen in a while."

After learning of the cause of her husband's death, Rita asked for a very important message to be passed on to his friends and family.

"Despite Alf being health and diet conscience you cannot in some cases outrun your risk factors," she wrote.

"Please if you have any concerns around your own health or you have a family history of cardiac issues, feel tired or have any irregular heart beats, fainting or pain please do not hold off seeing your doctor and also we urge you to have a stress test done as well as blood tests.

Please take care of your hearts because we heart you."

Tributes have been flowing in for Mr Nguyen from friends, family and those who knew him from the Sydney music scene.

A GoFundMe page has been set up to help his family following the unexpected passing. Photo / GoFundMe
A GoFundMe page has been set up to help his family following the unexpected passing. Photo / GoFundMe

Fellow DJ Alex Chung posted a heartfelt message to the Sydney Drum n Bass Facebook page informing people of Mr Nguyen's passing.

"On Saturday morning 13th July 2019 we all lost one of the legends of the Sydney DnB scene," Mr Chung wrote.

"Alf was Djing doing something that he loved and perform for the crowd, like he always did."

He went on to thank the people from the crowd who attempted to resuscitate Mr Nguyen when he collapsed.