TOKYO - Swimming superstars Katie Ledecky and Caeleb Dressel lead a powerful US team against a world-class field at this week's Pan Pacific Championships, hoping to gain valuable pre-Olympic experience in Tokyo.

Five-time Olympic gold medallist Ledecky arrives in Tokyo in spectacular form, after clinching the 200m, 400m and 800m freestyle titles at the US nationals last month and breaking her 14th world record in May. The 21-year-old will be the one to beat in those three events at the Pan Pacifics and also competes in the 1,500m freestyle.

In the 200m freestyle, Ledecky is poised for a heavyweight clash against Canadian teen sensation Taylor Ruck who bagged a record-equalling eight medals at this year's Commonwealth Games. Ledecky has clocked the two fastest times of the year over that distance but Ruck is only a few tenths of a second behind her and the race promises to be a thriller.

The high-class field also includes rising Japanese star Rikako Ikee, Ledecky's American rival Allison Schmitt and 17-year-old Australian Ariarne Titmus, who won a Commonwealth relay gold. The Australians will be hoping to build on their Commonwealth success on the Gold Coast -- where they preserved a meet win record that stretches back to 1978 -- against a US team that traditionally carries all before it in international competition. The Aussies feature Olympic Gold medallists Cate Campbell, who swims in the 50m and 100m freestyle, and Emily Seebohm, who competes in the 100m and 200m backstroke as well as the 100m freestyle.

Outside the pool, Seebohm has been embroiled in a high-profile and acrimonious break-up with Olympic silver medallist Mitch Larkin that has served as a distraction to the squad. The Australian team for the August 9-14 event also includes Rio Olympic gold medallists Mack Horton and Kyle Chalmers.

With just under two years to go until the Olympics, some of the world's top swimmers will be hoping to create positive memories to bring to the Japanese capital in 2020.

"Just the atmosphere of being in Tokyo and knowing in a couple of years you're going to be back there, hopefully, at the Olympics is something that's going to excite you," said 2016 US gold medallist Simone Manuel, who will swim against Campbell in the 50m freestyle.

To add to the feeling of an Olympic warm-up, the events in the Pan Pacific Championships mirror those at the Games. On the men's side, two-time Olympic gold winner Dressel will be hoping to turn around his form after a lacklustre effort at the US nationals.

He dominated the 100m butterfly but was beaten in the 50m freestyle and finished a disappointing sixth in what he called a "horrible" 100m free. "There's a lot left in the tank," said Dressel, who is racing in six events in Tokyo. In the backstroke, Ryan Murphy of the US will be hoping to repeat his clean sweep in the 100m and 200m that he achieved in Rio. He also swims in the 200m freestyle.

The US powerhouse team have won all 12 previous Pan Pacific meets and dominate the all-time medal list with 566 golds, ahead of Australia and Japan who trail a long way behind.

South Korea have not entered any swimmers as they prepare for the Asian Games in Jakarta which begin on August 18, while China appear also to have one eye on that event with 200m freestyle Olympic champion Sun Yang a notable absentee from their squad. Organisers will be keeping watch on an approaching typhoon projected to batter the Japanese capital from Thursday with high winds and torrential rain.