SYDNEY, Australia — The opening night at the Australian swimming championships and Olympic trials produced two world records today.

Stephanie Rice broke the world mark in the 400-meter individual medley, finishing in a time of 4 minutes, 31.46 seconds. That took 1.43 seconds off American Katie Hoff's mark of 4:32.89 set on April 1 at last year's world championships in Melbourne.

The 19-year-old took almost six seconds off her personal best time.

"I was so in shock," Rice said. "I saw my time ... but I did not think I would go that fast."

Later, Emily Seebohm broke the world record in the non-Olympic 50-meter backstroke. Seebohm finished in a time of 27.95 seconds, taking 0.05 seconds off American Hayley McGregory's mark set two weeks ago.

"The goal was pretty much all this season to get that world record ... I just had to go under 28 this time," Seebohm said.

McGregory set the previous mark in Austin, Texas, on March 7.