It's very much a two-horse race as it stands with Jamaica and Poland looking strongest - as expected - at the second handover.

Jamaica make a blistering start and their first runner, Roneisha McGregor, has swallowed up the ground between her and her Canadian counterpart.

But in the first heat, 2015 world champions Jamaica and 2017 bronze medallists Poland are involved.

They both had two finalists in the individual 400m final.

Great Britain's 4x400m team won a fine silver in London two years ago.

They've got a tough heat here - lining up alongside them are defending world champs the USA, who have Allyson Felix in their ranks.

This is Felix's first track season as a mother - she had pre-eclampsia and underwent an emergency C-section at 32 weeks to deliver her daughter just under a year ago.

She now holds the record for the most gold medals at the track and field World Championships after her victory as part of the mixed 4x400m relay team.

Image source, Getty Images

But before Laura Muir takes to the Khalifa track, there is plenty of relay action coming up first.

That starts with the women's 4x400m relay heats, and British Athletics have named their quartet.

• Zoey Clark
• Jodie Williams
• Jessica Turner
• Laviai Nielsen

Image source, British Athletics

Saj Chowdhury
BBC Sport in Doha

There are a few diversions knocking around Doha because of the marathon - it's traffic o'clock. Quelle surprise.

But it's not a bad crowd inside the Khalifa - the Ethiopian fans are back in their hordes so there should be quite a noise during the 1500m and 5,000m.

And...and...outside it feels like a hot British summer's day - even though it's dark here. About 28C.

That is good-ish news for the marathon runners who go off for their jog just before midnight. Fewer calls for the medical carts this week, I reckon.

BBC One

We are back on BBC One with Michael Johnson and Paula Radcliffe joining Gabby Logan in the studio.

You can also watch at the top of this page.

More from Laura Muir on BBC TV: “I set myself a target this year of medalling in Doha, that’s what I want to do,

"That would be absolutely amazing. If I could get on that podium, that would be fantastic and give me a lot of confidence going into Tokyo the year after."

Laura Muir speaking to BBC TV: "When you run well, year by year that pressure is going to get higher.

"I’ve shown that I’ve dealt with it really well. I’ve been favourite, gone in and delivered.

"Without the injury, I would have had very, very strong hopes of medalling, but I still think I can be in the shape to have the potential to medal.

"I think I’m a lot better now at dealing with hot conditions, so I’m confident that hopefully the Scottish weather won’t have tainted my ability to cope with the heat too badly."

Image source, Getty Images

The last Briton to win world 1500m gold was Steve Cram back in 1983.

And he claimed that victory after a month-long injury lay-off which left him unable to race in the build up to the championships.

I'm saying nothing...

Image source, Getty Images

Among those in final action tonight is Britain's Laura Muir. She claimed European gold in Berlin last year but had her Doha preparations hampered by injury.

She tore her calf while surging to 1500m victory at the Anniversary Games in July and had a 74-day lay-off before the heats earlier this week.

Muir has been in fine form, however, finishing third in her semi-final to secure a place in tonight's final.

Welcome back. There are seven medals going today in Doha and their respective finals will soon be getting under way.

• Men's shot put (18:05 BST)
• Women's triple jump (18:35)
• Women's 1500m (18:55)
• Women's 5,000m (19:25)
• Women's 4x100m relay (20:05)
• Men 4x100m relay (20:15)
• Men's marathon (21:59)

Right, we're going to take a short break to get ourselves limbered up for a huge evening on the track.

We'll be back at 17:30 BST for the 4x400m relay heats and to see if Laura Muir and co can add to the medal tally.

In a bit.

Big news at the end of the men's javelin qualies. Neither Olympic champion Thomas Rohler or 2018 Diamond League winner Andreas Hoffman have done enough to reach the final.

Fellow German Johannes Vetter qualifies with the biggest throw of the day - a monster 89.35m.

Of the 12 who have reached the final, only seven threw the automatic qualifying distance of 84m.

Image source, EPA

Here's how they'll line up for tomorrow's final.

Steve Backley
Two-time world javelin silver medallist on BBC TV

Jazz Sawyers will have to go back to the drawing board to find a way of jumping further.

It is a matter of being honest and transparent with your reasons. You have to have those deep soul-searching chats with yourself and your coach.

Abigail Irozuru goes straight over to Jazmin Sawyers and puts an arm around her after her long jump disappointment.

Well then!

A fine last jump from Chanice Porter of Jamaica, measuring 6.57m, and that takes her into 10th place and bumps Brittney Reese down to 13th place!

Reese, a seven-time world champion, will not feature in the final!

Shara Proctor has also passed on her last jump, with her eighth place nailed on.

She and Abigail Irozuru will be representing Britain tomorrow.