USA's five-time Olympic champion Ryan Lochte has expressed his delight after four world records were broken in the first two days of swimming at the World Championships in Kazan, Russia.

Sweden's Sarah Sjostrom smashed the world record that she set on Sunday as she won gold in the 100m butterfly final on Monday night.

Katinka Hosszu of Hungary put her name in the record books on her way to winning the 200m individual medley last night, while Lochte's teammate Katie Ledecky set a new world record in the 1500m freestyle heats.

"Unbelievable," Lochte told The AP. "I'm glad to see world records get broken. It gets more people behind swimming so that's awesome."

Lochte will compete in the men's 200m freestyle final later today.