The relay action comes thick and fast, we're into the first of two heats in the women's 4x100m.

Jamaica go in lane seven in this one.

Great Britain earned silver in Paris last summer, their best result at the Olympics since 1956.

The quartet in that final was Dina Asher-Smith, Imani Lansiquot, Daryll Neita and Amy Hunt - who so impressively won world 200m silver yesterday.

Bianca Williams and Desiree Henry ran in the heats and may feature here again.

2024 bronze medallists Germany go up against the Brits in heat two, while well-fancied Jamaica go in heat one.

Dame Jessica Ennis-Hill
Three-time world heptathlon champion on BBC TV

Dame Jessica Ennis-Hill on Great Britain failing to qualify for the women's 4x400m relay final: "We would expect them to qualify. We've seen the success of the team in previous years. Where did it go wrong for that Great British team?"

Image source, Getty Images

Greg Rutherford
Former world and Olympic long jump champion

Greg Rutherford on Great Britain failing to qualify for the women's 4x400 relay final: "I'll be totally honest that's not good enough and we have to put it into perspective.

"Yes, it's tough and conditions are hard but when there's that much focus on an event you can't come last in your heat at a world championships.

"The four girls that went out there they should be able to navigate a qualification. From my point of view, it's genuinely not good enough."

So, two horrendous results for GB in successive relay heats after the women's 4x400m team finished last in their race.

In the BBC studio, 2012 Olympic gold medallist Greg Rutherford has not pulled his punches...

From heat two, Ghana are the shock winners after setting a national record.

Netherlands take second, while there is a roar of delight in Tokyo as Japan qualify third.

That was a chaotic race.

South Africa also DNF after the man in the lane next to them at the first changeover - Italy's 2020 100m Olympic gold medallist Lamont Jacobs - impeded their athlete. They will surely appeal there.

OH NO!

GB were in a good position to qualify, however they mess up the final changeover and are out of contention.

Eugene Amo-Dadzie, who was running the final leg for GB, set off far too early. Jona Efoloko had no chance of catching him for a legal changeover.

An absolute nightmare.

Image source, Getty Images

On your marks.

See you on the other side...

Jeremiah Azu will run the first leg for GB. He has disposed of his "100% Jesus" headband that he wore earlier in the championships, which got him into hot water with World Athletics.

A note on that USA team - they still have Noah Lyles to come in for the final.

They are the men to beat.

As in the men's 4x400m, the fall of a favourite could open the door for Great Britain.

Jeremiah Azu, Louie Hinchcliffe, Jona Efoloko and Eugene Amo-Dadzie are the GB team who will run in heat two.

Kishane Thompson reached back for the baton to run the final leg for Jamaica... but it simply wasn't there.

After messing up in the Olympics, the Jamaicans have fallen short again in the World Championships.

Image source, Getty Images

Another big upset!

Jamaica, featuring individual 100m champion Oblique Seville, messed up their final handover and are out of the race.

Canada, the Olympic champions, are safely through as are the strong USA team. Germany take a surprise third place.

Great Britain's team after failing to qualify for the women's 4x400m relay final:

Poppy Malik: "I was hoping to get the team in the mix, I didn't run as fast as I wanted but I gave it everything I had."

Nicole Yeargin: "I tried my best. It's been a long championships and hopefully we can come back next time and come back to our form and how we're supposed to be."

Yemi Mary John: "We are incredibly disappointed, like Nicole said. We live to run another day."

Victoria Ohuruogu speaking to BBC Sport after Great Britain finish last in their heat and are out of the women's 4x400m relay: "It's a huge disappointment. We gave it everything we had. It's been a long championships.

"I just want to say a huge thank you to the National Lottery and to the Team GB staff. Unfortunately, we couldn't deliver today but overall it's been a good championships for Team GB, so we're really grateful."

Image source, PA Media

Great Britain won bronze in Paris and will hope for a similar result in Tokyo on Sunday.

Zharnel Hughes ran in the 200m final last night - but is back again here for the heats.

They will go in heat two, alongside Olympic silver medallists South Africa.

In heat one, the USA will look to follow up the world title they won two years ago - and banish memories of an Olympic nightmare.

The Americans were disqualified for an illegal baton exchange in the 2024 final – the 12th time in the past 23 major global championships they have missed out on the title due to a dropped baton, botched handover or other transgression. After messing up in the 4x400m, the pressure is on.

Jamaica won world bronze in 2023 but messed up themselves in their heat at the Olympics.

A bit of news from the men's 4x400m heats - both Australia and Brazil have been disqualified for illegal handovers.

That doesn't impact the Brits, they are still through to the final.

Harry Poole
BBC Sport in Tokyo

Before the final 800m event of the world heptathlon, Katarina Johnson-Thompson is on 5578 points - within 84 points of third-placed American Taliyah Brooks and 165 points behind Ireland's Kate O'Connor.

So, what does it all mean?

Johnson-Thompson has an 800m personal best which is 8.5 seconds quicker than Brooks', whom she will need to beat by about six seconds to get bronze.

American Anna Hall, with the fastest 800m time in the field, is 122 points clear of O'Connor and poised to win her first global heptathlon title.

Hall's 800m personal best of 2:01.23 equates to 1097 points - which would give her a final total of 6,962.

Johnson-Thompson ran 2:04.90 (1041 points) on her way to Olympic silver last year, which would put her on 6,619 overall and in bronze medal position based on personal best times.

O'Connor looks very much on course for silver. She has a PB of 2:10.46 and those 958 points would keep her clear of Johnson-Thompson on 6,701.

Brooks, who has run 2:13.39 (916 points), who would theoretically finish fourth on 6,578.

Anyone else's head hurting?

The United States close out the second half of heat two, with Britton Wilson finishing some way ahead of the rest of the field.

Belgium and the Netherlands finish second and third, while France's time in fourth is good enough to progress as a fastest non-automatic qualifier.

Italy join them from the first heat, with the French quartet knocking out Spain.