PHOTOS: Records tumble as Team USA enjoy huge night

American swimmers smashed records and grabbed gold at the world championships on Friday, with sprint king Caeleb Dressel taking down Michael Phelps' 100 metres butterfly world record and teenager Regan Smith lowering the women's 200 backstroke mark.

Russia's Anton Chupkov got in on the act, setting a world record of 2:06.12 in the final of the men's 200 breaststroke.

Dressel, who in 2017 tied Phelps record of seven world titles at a single championships, knocked 0.32 seconds off his former team mate's butterfly mark set at the world championships in Rome 10 years ago.

"Records are meant to be broken. I hope he was happy watching me do that," Dressel, who swam the semi-final in 49.50, said of the Olympic great.

"I don't want to hype myself up in any way, shape or form, it can be a scary thought to do something that's never been done before. I woke up today and I wanted to do it.

"I thought I was ready to do it."

The 22-year-old has already won three golds in Gwangju and is on course to repeat his haul of seven world titles, a feat that not even Phelps managed.

Even if someone somehow beats Dressel to gold in the 100 butterfly final, he is happy in the knowledge that he once had his name in the record books.

"Just to have that one little moment where I claimed I was the best at one point in the history of swimming is very special."

Dressel also paid tribute to 17-year-old team mate Smith, who swam 2:03.35 to beat compatriot Missy Franklin's mark of 2:04.06 set at the 2012 London Olympics.

"That was phenomenal," he added. "That was one of the top three toughest world records on the women's side and she just crushed it."

Smith was in a state of shock.

"I didn’t think I’d ever do that," said Smith. "It’s crazy but I am very happy with what I was able to do."

Simone Manuel, defending champion in the women's 100 freestyle, had squeaked into the final with the joint slowest time, putting her in unfavoured lane one for the blue riband race.

Yet while Sweden's Sarah Sjostrom and Australian Cate Campbell battled tooth and nail from the middle lanes, the American stormed home under the radar to grab the gold in a personal best 52.04.

"I did feel a lot of pressure coming into the meet," she said. "I think a lot of it was on myself wanting to repeat, but I'm really happy with a best time and the win."

Manuel had swam the anchor leg for the Americans in the mixed 4x100 medley relay on Wednesday when she gave up a sizeable lead to Cate Campbell as Australia pipped the United States to gold by 0.02 seconds.

That did not sit well with Manuel.

"This week has been a bit of a roller-coaster for me, not all of my swims have been what I would have liked them to be and I did take that relay really hard," she added.

"I just needed to regroup and put on a good face ... I'm a veteran on the team so I have to be able to show a little bit of poise in these hard moments."

Silver medallist Campbell, who took a year off from swimming after she struggled with the disappointment of failing to medal at the Rio Olympics, said even if she had been swimming next to Manuel she would not have beaten her.

But with the 2020 Olympics just a year away, not going in as world champion may have its advantages, she said.

"I think it will be great for me going into Tokyo without a huge target on my back," she added. "I think I’ve well and truly shifted the focus away from that now so it’s great to be back and great to be mixing it with the best in the world."

American freestyle great Katie Ledecky, who surrendered her 400 title to Australia's Ariarne Titmus on Sunday and pulled out of the 200 heats and 1,500 final for medical reasons, was back in the pool for the 800 on Friday and qualified for the final in second place behind compatriot Leah Smith.

Ledecky did not take reporters questions afterwards.

With Lilly King missing from the 200 breaststroke final after being disqualified from her heat on Thursday, the path to gold was clear for her rival Yuliya Efimova and the Russian, who served a 16-month suspension for doping, breezed to the title.

Also winning gold on Friday was the Australian men's 4x200 relay team, who came home in 7:00.85 ahead of Russia and the United States.