Gwangju - American Caeleb Dressel retained his world men's 100 metres freestyle crown on Thursday, collecting his third gold medal of the week.

The 22-year-old, who swept to seven world titles two years ago, clocked a blistering 46.96 seconds in Gwangju to win swimming's blue riband event in the second fastest time ever, with Olympic champion Kyle Chalmers taking silver.

Dressel high-fived Australian rival Chalmers before perching himself on the lane rope as he milked the applause, raising a fist to flag-waving American fans.

Chalmers touched in 47.08 with Russia's Vladislav Grinev the best of the rest in 47.82.

Rio gold medalist Chalmers came into the world championships on fire, but Dressel exploded from the blocks and was half a body length in front at the turn.

Chalmers tried to fight back, but Dressel had too much of a lead and the tattooed pin-up romped home to claim his fourth medal of the week.