American clocks 48.29 as Amber Anning finishes runner-up behind her in a swift 49.38.

Sydney McLaughlin-Levrone smashed the American 400m record while Amber Annning came close to beating her own British record in some red-hot semi-finals on Tuesday night at the World Championships in Tokyo.

McLaughlin-Levrone has switched from 400m hurdles to 400m flat for these championships and it looks to be paying off as she scorched to 48.29 to beat Sanya Richards-Ross’s US record of 48.70 from 2006.

McLaughlin-Levrone, 26, is now No.7 all-time in the event as she beat her own PB by 45 hundredths of a second.

Anning, meanwhile, finished strongly to be runner-up in the same heat in 49.38 and she will look to beat her 49.29 UK record in the final.

McLaughlin-Levrone said: “This race definitely gives me confidence for the final. I just want to go out there and execute well again. I didn't expect to run this fast today. I still have more to show. I feel strong and good, and have confidence in my fitness. I will give everything I have in the final."

Anning said: "It's my best race of the whole year. I was grateful, very happy and executed it. I think my confidence was there, which is something I've been missing this year. But I put it all together today. It was about having faith in my ability.”

Salwa Eid Naser, the 2019 world champion from Bahrain, was another semi-final winner in 49.47, while reigning champion Marileidy Paulino of Dominican Republic was passed in the final strides in her semi by Natalia Bukowiecka as the Pole won in 49.67.

There was no luck for Anning’s team-mates Yemi Mary John and Victoria Ohuruogu, though, as they clocked 51.51 and 51.65 respectively to finish last in their heats.

Botswana athletes were in inspired form in the men’s 400m semi-finals as Busang Collen Kebinatshipi led the qualifiers with a world leading 43.61. He will be joined in the final by two team-mates, too, as Bayou Ndori clocked 44.21 and Lee Eppie 44.51.

The British men went out, though. Matt Hudson-Smith, the Olympic silver medallist, finished sixth in his heat in 44.95. Charlie Dobson was seventh in his heat in 44.85 but said overall his season had been a success with a London Diamond League win where he ran a big PB of 44.14.

Sam Reardon was eliminated after clocking 45.10 for eighth in his heat.