Regan Smith set the 100 metres backstroke world record at the US Olympic trials in Indianapolis on Tuesday, touching the wall first in 57.13 to shave 0.2 seconds off Australian Kaylee McKeown's previous mark.

With just over a month to go before the Games, Smith's win in the final sealed her place on the US team and sets up a Paris showdown with McKeown, who swam 57.33 in Hungary last year.

"I'm so proud of myself," Smith said.

"Backstroke is hard for me sometimes but to fight back like this and get that back means a lot."

Katharine Berkoff was second with a time of 57.91.

Smith, a three-time Olympic medallist who took bronze in the event at the Tokyo Games, still has two more events to contest at the trials.

It's the second world mark to fall at Indianapolis after Gretchen Walsh smashed the record in the 100 metres butterfly on Saturday, an event in which Smith also swam and set a personal best time. (Agencies)