Michael Phelps broke his fifth world record in a week on Sunday to collect his seventh gold medal at the world championships and stake his claims to be the greatest swimmer of all time.

The 21-year-old American wiped more than two seconds off his own world mark for 400 metres individual medley to better Ian Thorpe's haul of six gold medals at the 2001 world championships.

Phelps was robbed of his chance for an unprecedented eighth gold, which would have eclipsed Mark Spitz's seven at the 1972 Munich Olympics, when the US were disqualified from the medley relay after Ian Crocker left the blocks too early during the morning heats.

Phelps, who was officially named as the best male swimmer in Melbourne, did not swim in the heat in order to save himself for the final but was reluctant to criticise his team mate.

"Team USA goes into a meet as one, and that's how we're going to exit," Phelps said in a poolside interview.

"Everything can't go perfect so it's all about how you adapt from these things and learn from your experiences."

Phelps had already won the 200 medley, 200 freestyle, 200 butterfly, 100 butterfly and two relays and made it seven from seven with a runaway victory in the 400 medley.

His time of four minutes 06.22 seconds slashed 2.04 off the previous mark of 4:08.26 which he set at the 2004 Athens Olympics and a gave him a comfortable win over fellow American Ryan Lochte and Italian Luca Marin.

Katie Hoff, who used to train with Phelps at the North Baltimore Aquatic Club, broke the world record to win the women's 400 medley and claim her fourth world title before her 18th birthday.

Hoff stormed home over the closing freestyle leg to touch the wall in 4:32.89, 0.70 under the old mark set by Ukraine's Yana Klochkova at the 2000 Sydney Olympics.

Jessica Hardy won the women's 50 breaststroke as the US scooped up three of the seven golds on offer to finish at the top of medals table with 21 golds, including 20 in the pool.

Laure Manaudou of France was named as the outstanding female swimmer after winning the 200 and 400 freestyle, finishing second in 800 freestyle and 100 backstroke and a third in the 4x200 freestyle relay.

FINAL NIGHT

Australia won two more golds on the final night, including the men's medley relay, to finish the competition with nine wins in the temporary Susie O'Neill pool, which was installed in the Rod Laver tennis centre but will be dismantled on Monday.

Libby Lenton signed off by winning the 50 freestyle final in a slick 24.53 to defend the title she won in Montreal two years ago and join American Tracey Caulkins (1978) as the only women to win five gold medals in a single world championship.

"If someone had told me I would have won five gold medals I would have pretty much have laughed in their face," said the 22-year-old, who is getting married next week.

There was disappointment for the hosts when Grant Hackett's long stranglehold on the 1500 freestyle came to a shuddering halt.

Unbeaten for a decade, Hackett went into the championships under an injury cloud and could only manage seventh place as Polish teenager Mateusz Sawrymowicz stormed to the gold in 14:45.91.

"Every athlete goes through difficult times in their career," Hackett said.

"I am proud of myself for getting up there. People thought I had plenty to lose but I had nothing to lose."

Gerhard Zandberg won the men's 50 backstroke in 24.98 to provide South Africa with their second gold medal of the week following Roland Schoeman's win in the men's 50 butterfly.