The US Olympic Track and Field Trials got off to an electrifying start on Friday, as 2016 gold medallist Ryan Crouser shattered the shot put world record and six-time gold medallist Allyson Felix began her quest to reach a fifth Games.

Crouser exceeded fellow American Randy Barnes' 31-year-old record by 25 centimetres with a 23.37-metre throw, letting out a roar inside the newly renovated Hayward Field in Eugene, Oregon, to wild applause from fans.

"The second it left my hand I knew it was good," he told reporters.

Felix, 35, the United States' most decorated female track athlete, put up an age-defying performance to win her 400m heat in 51 seconds, as her two-and-a-half-year-old daughter Camryn watched and cheered from the stands.

"I'm taking everything in, not taking anything for granted. It's been a long journey," said Felix, who has stated this will be her last Olympic trials. "I feel at peace with everything and I feel very prepared."

Felix, who has picked up 13 world championship medals across her dazzling, nearly two-decade-long career, said she was savouring the time she gets to compete in front of Camryn, before she retires.

"Initially I was so disappointed with everything getting postponed, and then I began seeing all of the silver linings," said Felix. "She's just so aware."

Already a star at age 21, Sha'Carri Richardson proved she was worth the hype as she recorded a blistering 10.84 in the 100m, the top time in the event, despite her shoe coming untied during the race.

"I'll be sure to lace them and tuck them for the next rounds to come," said Richardson, who achieved a 24.1 mph (38.8 km/h) top speed during the sprint.

"To win the Olympics, I'm gonna say it could take a world record," she added. "There are so many phenomenal names that are predicted to be at the Olympic Games."

Elsewhere in the day's action, reigning world champion Donavan Brazier clinched his 800m heat in 1:45, as expected, and 2016 bronze medallist Jenny Simpson, 34, won her first-round heat in the 1,500m in 4:11.34, as she bids for a spot in her fourth Games.