Jamaica off to a blistering start. Not a good first changeover for GB.

Ready for this?

It's under way.

Michael Johnson
Four-time Olympic gold medallist athlete on BBC TV in Doha

Totally disagree with the choice. Dina should be on the anchor to give yourself the best chance to be in the mix.

Light show time.

Sounds like there are a lot of British fans in Khalifa Stadium. Big cheers as the GB team is introduced.

GB are in lane six, with the USA on their outside.

Jamaica are in lane four.

This is going to be so good.

Now that Dina Asher-Smith is running the second leg, she will go head-to-head with Jamaica's Shelly-Ann Fraser-Pryce.

Interesting.

Next up, the women's 4x100m relay final and GB's line-up has been changed. It now looks a little like this...

• Asha Philip
• Dina Asher-Smith
• Ashleigh Nelson
• Daryll Neita

Britain were silver medallists in London two years ago. What will it be in 2019?

BBC Sport

Women's 1500m champion Sifan Hassan speaking to BBC TV: "It's a very hard week for me [because her coach Alberto Salazar was banned for doping violations], I was so just angry and I could not talk to anyone. I just ran all out. That hard work can't be beaten by anything.

"It's what makes me angry, I have been clean all my life. I work hard, I'm not an emotional person but it makes me so mad."

Eilish McColgan speaking to BBC TV: "I tried my best to make it a hard race from the start. Those girls who ran PBs need to credit me for my pace-setting.

"I'm a little disappointed with my time. I wanted to run 14:40 or thereabouts. I was a couple of seconds off that. I started to feel it on the last kilometre.

"They're the best in the world, that's why they're here.

"We both ran PBs today, so I guess that's all we can ask for but you always want that little but more from yourself."

A very tearful Sifan Hassan has been talking to the BBC about her 1500m victory.

She says she's mad and angry about "what people have been saying".

Her coach, Alberto Salazar, was this week given a four-year ban for doping violations.

Michael Johnson
Four-time Olympic gold medallist athlete on BBC TV in Doha

It's an opportunity. I don't know what to say. They are in the final by default.

Can they make anything of that in the final? This team don't seem to have the pop.

Well then.

Earlier we saw Great Britain's men miss out on a fastest losers spot in the men's 4x400m relay.

However, Botswana, who qualified sixth, have been disqualified, meaning GB will feature after all.

Image source, Getty Images

Laura Weightman speaking to BBC TV: "I'm really pleased with the race. I'm a little frustrated, I know I'm in brilliant shape at the moment but when those girls put a surge in, in the middle of the race it's a little bit ahead of me now but it's a place I think I can get to.

"I'm delighted to run a PB but I want more."

11 of the top 14 in that final clocked personal bests.

Astonishing pace. A joyous Hellen Obiri is off around the track to celebrate retaining her world title.

Dennis Ethan: No Kenyan athlete has made me proud like Hellen Obiri tonight, a determined finish

Lee Fergusson: Hellen Obiri is just unbelievable

Without stating the obvious, that looked absolutely knackering.

Hellen Obiri barely had the energy to lift her arms in celebration as she crossed the line.

It's a Kenyan one-two, with Margaret Chelimo Kipkemboi taking silver and Konstanze Klosterhalfen taking bronze.

In a punishing race, Laura Weightman runs a personal best of 14:44.57 to finish seventh, with Eilish McColgan 10th in 14:46.17. That's a PB for McColgan, too.

Andrew Cotter
BBC Sport commentator in Doha

That was a good race. A great effort from both the British girls but it is just that the greatness of Hellen Obiri was too good once again.

Klosterhalfen can't keep up with Obiri and she's going to take the gold...