American Caeleb Dressel breaks Michael Phelps’s world record in men’s 100m butterfly at World Championships

American Caeleb Dressel set a world record of 49.50 seconds in the semi-finals of the men’s 100 metres butterfly at the world championships in Gwangju on Friday.

Dressel shaved 0.32 seconds off Michael Phelps’ former record of 49.82 set at the 2009 worlds in Rome.

The sprinter, who already has three gold medals in Gwangju, is set to swim in the 50 freestyle semis later on Friday.

Another American Regan Smith also set a world record in the semi-finals of the women’s 200 backstroke at the world championships in Gwangju on Friday.

Smith, 17, then gave the United States its second record of the evening when she swam 2:03.35 to take 0.71 seconds off compatriot Missy Franklin’s mark set at the 2012 London Olympics.