The rivalry between Chinese and Japanese swimmers at the short-course world championships foreshadows an intense pool battle at the 2020 Tokyo Olympics.

Tuesday's opening night of the 25m worlds in Hangzhou provided no shortage of thrills with a string of world and continental records shattered, but it was the battle between the host and its main Asian rival that stole the show in and out of the pool.

At the center of the spotlight was Japanese men's medley specialist Daiya Seto, who edged South Africa's Chad Le Clos and China's Li Zhuhao to set a new short-course world record of 1min, 48.24sec in the 200m butterfly.

To focus on the 200 fly, Seto gave up the 200 individual medley scheduled in the same session, which was won by Chinese star Wang Shun. But the 24-year-old native of Moroyama in central Japan vowed to try to make up for it in his strength event, the 400 IM, on Saturday.

"I always want to break the record at any meet I enter, so I will try to do it again in the 400 IM," said Seto, a two-time long-course 400 IM world champion (2013 and 2015).

"It's a pity that I missed the 200 IM; hopefully I can have another head-to-head fight with Wang in the event at the next competition."

Wang, also a medley swimmer having registered for the 400 IM in Hangzhou, rose to the challenge without hesitation.

"Seto is a strong competitor. A race against him is always exciting and usually brings out the best in me," said Wang, who became the first Chinese man to defend a short-course world title with the 200 IM victory.

"I will try to improve my form and put out my best performance to race against him in the 400."