The first track and field world record has been broken by USA in the mixed 4x400m relay.

The quartet of Vernon Norwood, Shamier Little, Bryce Deadmon and Kaylyn Brown clocked 3:07.41 to smash the previous mark - set when the USA won the world title in Budapest last year - by more than a second.

Norwood put the US team into an early lead, then Little extended it on the second leg. Deadmon opened up a significant gap on the chasing pack on leg three, then Brown anchored them to a clear victory, crossing the line more than three seconds ahead of France, who set a national record of 3:10.60. Belgium was third in 3:10.74, also a national record.

The record is subject to the ratification procedure.