Chinese teenager Pan Zhanle broke the men's 100m freestyle world record with a time of 46.80sec at the world championships in Doha on Sunday.
Pan achieved the new mark leading off his team during the 4x100m freestyle relay to set up teammates Ji Xinjie, Zhang Zhanshuo and Wang Haoyu to seal gold for China in 3 minutes 11:08 seconds.
The 19-year-old shaved 0.06sec off the previous record of 46.86 achieved by Romanian David Popovici at the European championships in Rome in August 2022.
"Yeah, it was an incredible time. I trusted my friends and we did our best," Pan said.
"I said to myself 'swim hard'. I was shocked when I saw the time, I didn't expect to break the world record now, I wanted to keep it for the Paris Olympics."
Italy took silver in 3:12.08 and the United States bronze in 3:12.29.
Before these worlds Pan had only one world medal, silver in the 4x100m medley relay last year in Fukuoka, Japan.
He also has three Asian Games titles, including the 100m. His previous personal best was 46.97, which made him the fifth fastest man in the world before arriving in Qatar.
The Netherlands won the women's 4x100m freestyle relay as the quartet of Kim Busch, Janna van Kooten, Kira Toussaint and Marrit Steenbergen clocked 3:36.61
Australia took silver, 0.32sec adrift, with Canada completing the podium.
Earlier South Korea's Kim Woo-min won gold in the men's 400m freestyle on the first day of the swimming competition.
Kim clocked 3:42.71 to edge out Australia's Elijah Winnington, the 2022 world champion. Germany's Lukas Martens took third place.
The 22-year-old Kim was on course to break Paul Biedermann's world record going into the final 100m but couldn't maintain the pace and finished over two seconds off the German's mark, set in 2009.
Olympic champion Ahmed Hafnaoui of Tunisia was a surprise casualty in the heats, coming a lowly 17th overall and missing out on a place in the final.
New Zealand's Erika Fairweather cruised to victory in the women's 400m freestyle, touching the wall over two seconds clear of China's Li Bingjie.
Isabel Gose of Germany claimed the bronze.