Brazil's Cesar Cielo Filho sliced through the 47-second barrier to triumph in the men's 100 metres freestyle final amid another torrent of swimsuit-aided records at the world championships in Rome on Thurday.

The Brazilian stormed to a world record time of 46.91 to stun Olympic champion Alain Bernard, who came in second ahead of compatriot Frederick Bousquet.

"I saw Bernard in the last 25. I was hurting a lot but I thought he was hurting too because he wasn't catching me," Cielo Filho told reporters after beating the absent Eamon Sullivan's Beijing Olympic mark of 47.05.

"I think the first 50 metres was the key to the race. I think today was just my lucky day."

It was a bitter moment for Bernard, who had breached the 47 second mark at the French championships in April but his time was not ratified because his hi-tech swimsuit was not approved.

Polyurethane suits will be banned from next year after controversy over the scores of world records they have prompted, seven being shattered on Thursday to bring the total number for the championships to a staggering 29.

The worlds, which end on Sunday, will stand out in the swimming annals with many wanting asterisks to be put by records set in the suits, knowing they could take years to break when the sport returns to mere textile costumes.

American Ryan Lochte smashed the first world record of the day in the Foro Italiaco's open-air pool to win the men's 200 individual medley final.

Lochte shot through the water in one minute 54.10 to beat Michael Phelps' Beijing Olympic time of 1:54.23.

"The swim felt great," he beamed. "I went out there as fast as I could and I just held on for dear life."

Three-times champion Phelps decided not to defend his title this year after scaling back his programme for these championships, allowing 2007 silver medallist Lochte to poach his crown and record.

Hungary's Laszlo Cseh, second three times to Phelps in Beijing, again took silver.

"Every time I look up I see an American," he scowled.

While Cielo Filho was still celebrating poolside, Australian Jessicah Schipper steamed to the women's 200 butterfly title with a world record time of 2:03.41 after Mary Descenza had lowered the mark in Wednesday's heats.

The lively Roman crowd have become accustomed to previously unsurpassed times but Australian Christian Sprenger's world record of 2:07.31 in the men's 200 breaststroke semi-finals was a surprise given the competition around him.

Canada's Annamay Pierse also shattered the women's 200 breaststroke world record in her semi.

The women's 50 backstroke world record was ripped up for a third time this week, China's Zhao Jing settling matters with 27.06 to seize gold in the final.

China, who picked up their first male world championship swimming gold on Wednesday through Zhang Lin, continued to make a splash with the women's 4x200 metres freestyle relay team surging to gold in a world record time.

The quartet of Yang Yu, Zhu Qian Wei, Liu Jing and Pang Jiaying won in seven minutes 42.08 seconds, more than two seconds better than Australia's mark of 7:44.31 from the Beijing Olympics.

Despite world record holder Britta Steffen and defending champion Libby Trickett competing, the women's 100 freestyle mark stayed in tact in a comparatively slow semi-final where the big names all got through.

American Aaron Peirsol, dumped out in the 100 backstroke semis despite being Olympic champion, partly made up for his disappointment by setting a championship record and qualifying first for Friday's 200 backstroke final.