China's state media, athletes and netizens rallied to support Olympic swimming champion Pan Zhanle after critics including an Australian swim commentator said his world record swim in the 100 metres freestyle was not "humanly possible".

Pan smashed his own 100 metres freestyle world record, shaving 0.40 seconds off the previous mark he set at the World Championships in Doha in February, to humble rivals including Australia's Kyle Chalmers and Romania's David Popovici.

The 19-year old Pan finished in 46.40 seconds to take China's first swimming gold medal at the Paris Olympic Games. His win came after he "completed rigorous doping test programs prior to and during the games with zero positive results," the China Daily said on Friday.

Pan said he took 21 doping tests from May to July prior to the games. "I cooperated with all the testing procedures and stayed confident that I am competing fair and clean," he told the newspaper.

"I did a lot of aerobics and endurance training to strengthen my push and kick in the final split. We have also adopted a scientific underwater monitoring and analysing system to review our techniques and strokes, so that we can train better and more effectively."

Australian coach and commentator Brett Hawke posted on his Instagram that "It's not humanly possible to beat that field" and that the swim was "not real life. Not in that pool, against that field."

Hawke's comments were widely shared on China's Weibo platform with one user commenting: "It's so cool to see them incompetent, angry and breaking their defences."

"He is praising us, saying that position is impossible but sorry we did it," said another.

The Chinese swim team has been under intense scrutiny since revelations in April that 23 of the country's swimmers tested positive for a banned heart medication in 2021 but were allowed to compete at the Tokyo Olympics.

The World Anti-Doping Agency (WADA) accepted the findings of a Chinese investigation that the results were due to contamination from a hotel kitchen, and an independent review backed WADA's handling of the case.

A World Aquatics audit concluded there was no mismanagement or cover-up by the governing body. Pan's name was not among the Chinese swimmers listed in the reports by the New York Times and German broadcaster ARD.

"The Chinese swimming team underwent more tests in two weeks than foreign athletes did in an entire year," China's Global Times Newspaper wrote.

Chinese swimmer Zhang Yufei, who won the bronze medal in the women's 200 metre butterfly final, responded to questions about Pan during a press conference on Thursday.

"Why are Chinese athletes questioned when they swim so fast? Why didn't anyone dare to question Phelps when he won?"