In short:

Cameron McEvoy has broken the men's 50 metres freestyle world record in China.

McEvoy, the Olympic and world champion, set a time of 20.88.

Brazil's César Cielo's had held the previous world record of 20.91 since 2009.

Australia's Cameron McEvoy has broken the men's 50 metres freestyle world record, which had stood for 17 years.

The reigning Olympic and world champion posted a time of 20.88 seconds at the China Swimming Open in Shenzhen, clipping 0.03 off Brazilian César Cielo's previous mark.

Cielo set his world record of 20.91 during swimming's 'super suit' era in 2009.

McEvoy is the first Australian to achieve the feat since Eamon Sullivan lowered the world record three times in 2008.

"I knew I had a chance to do a PB (personal best)," McEvoy said.

"My old PB was 21.06, so maybe 20.99? But doing ⁠20.88 is unreal. It's crazy.

"The 50 metres, I look at it as a strength-based skill. It's different to the other events in swimming.

"A lot more strength and power is involved, and men peak in strength into their 30s — well into their 30s."

Cielo was quick to congratulate McEvoy on social media, tweeting: "Congrats, Cam. Lightning fast swim! Incredible!

"I saw a phrase a while ago that perfectly captures what you've been doing.

"You never change things by fighting the existing reality. To change something, build a new model that makes the existing model obsolete. Congratulations!"

This was a reference to McEvoy's famed new approach to swimming training, in which he spends more time in the gym rather than in the pool.

Cielo's record was set when high-tech swim suits were the norm, but they have since been banned.

AAP/Reuters