China's Olympic champion Sun Yang advanced into finals as a frontrunner in the men's 400m freestyle on the first day of swimming competition at the 18th FINA World Championships here on Sunday.

Sun finished in three minutes and 44.10 seconds in the preliminaries, launching a quest to win his fourth consecutive world championship title in the event.

"It is always difficult to swim the first race, and everyone is the same. My goal in the morning is to make the final and do what I should do," Sun said.

"I trained very hard this year. I want to show my best in every race I compete in. It is a good rehearsal for next year's Olympic Games," the three-time Olympic gold medalist added.

Danas Rapsys of Lithuania finished second in 3:44.31, and Jack Alan Mcloughlin of Australia came next in 3:44.79.

Among 47 competitors, China's Ji Xinjie sealed eighth to punch the last ticket to the finals slated in the evening.

The swimming events of the Gwangju worlds began on Sunday, with a total of 42 gold medals up for grabs in the pool. The first four golds will be awarded on the first day.

Team China sent a squad of 43 swimmers to the Gwangju worlds.