EUGENE (AFP/REUTERS) - Allyson Felix booked her place at next month's Rio Olympics on Sunday with the fastest 400-metre time in the world this year at the US track and field Olympic trials.

Felix, who has been hampered by an ankle injury following a freak training accident in April, powered home to win the final at Hayward Field in 49.68 seconds.

She was joined by Phyllis Francis in second and Natasha Hastings in third.

The 30-year-old from Los Angeles is aiming to become only the third woman after Valerie Brisco-Hooks of the US in 1984 and Marie-Jose Perec of France in 1996 to have won the 200m and 400m in the same Games.

Felix competes in the 200m starting next Friday.

LaShawn Merritt powered home in 43.97 seconds for the men's 400m victory - also the fastest time set this year.