GOLD COAST (AFP) - Katie Ledecky smashed another world record as Michael Phelps claimed his first individual gold medal post-retirement at the Pan Pacific Championships in Australia on Saturday.

American swimming wonder teen Ledecky set the first world record of the Gold Coast meet, shaving almost half a second off the 400-metres freestyle mark she set at this month's US Championships.

The 17-year-old schoolgirl clocked three minutes 58.37 seconds to eclipse her previous mark by 0.49sec.

While it was Ledecky's fourth title of the championships, Olympic legend Phelps secured his second gold when he took out the 100m butterfly from team-mate Ryan Lochte.

Phelps, 29, who was a member of the US's winning 4x200m freestyle relay team on Friday, shaded Lochte by 0.38sec in winning the butterfly event in 51.29 adding to his haul of international titles just four months into his comeback.