All change again in the men's wheelchair race, and it's shaping up for a great finish.

The Japanese racers are so strong, and Hiroki Nishida has taken the lead as we build up to the sprint finish. Marcel Hug has slipped down into third but David Weir is still sitting on his shoulder.

Lots of you feeling motivated by the runners today - could you be taking part next year?...

Image source, @DonnaMaughan15

Image source, @MariaVictoriaPV

Huge whoops and cheers for Mary Keitany as she reaches Tower Bridge.

There's so many people on the streets, cheering, waving clappers. Keitany is still pushing herself all the way but she's starting to show signs of slowing after a ferocious start.

Alyson Dixon is still the leading Briton in 17th, with Jo Pavey in 25th.

This is an early contender for my favourite marathon picture of the day - Ore Oduba, talking to a marathon runner dressed as Mr Potato Head. 

They were team-mates at the London Games and again in Rio - but that's going out of the window today.

Now they've conquered the water, Heather Stanning and Helen Glover are looking for other challenges, and they're racing in their first London Marathon.

Stanning is running for the Royal British Legion Industries and Glover for the Brain and Spine Foundation.

And their biggest motivation? The desire to beat each other, of course...

It could be a close finish in the men's wheelchair race!

At the 35k mark, Marcel Hug has taken the lead again, after a surge from Ryota Roshina. David Weir, meanwhile, is keeping a close eye on Hug. 

He's in second and he's staying close to Hug. Heads down, arms pumping, complete focus. They are around ten minutes from the finish.

Image source, BBC Sport

Dawn Hamer: Good luck to Cath Moss today, running her first ever Marathon for Chron's and Colitis UK from all your colleagues t N-Compass Norhtwest.

Sarah Simon: Emma Bish is running today to raise money for the church where John Disley the marathon founder is buried. Emma works with his daughter Kate at Milverton Primary School in Leamington Spa. And her dog Henry wishes her good luck!

Image source, Sarah Simon

Henry is adorable! 

Go, Baasit, go!

Watch Gogglebox's Baasit Siddiqui run the marathon live on BBC Sport Facebook and send him your support. #getinspired    

In the women's elite, Mary Keitany is keeping up a brutal pace. She's barely slowed down since the start. In fact this entire pack is going at a remarkable speed.

She's been helped along by some kids, who are trying to keep pace with her on the side of the road. She looks comfortable, too.

An utterly, utterly glorious sight.

Go well, folks. 

The Royals press the buzzer - and off they go!

The 37th London Marathon is under way. Good luck to all of you wonderful people. An absolute sea of bibs charging up the start line.

Ellie Thomason
BBC Sport at London Marathon

I've just been speaking to Graham. He was aiming to run today's marathon in four hours but the time isn't important anymore. He lost his dad to pancreatic cancer last night. 

Image source, BBC Sport

It's almost time. 40,000 people swaying together on the start line. All those months of training, of hard work - it's all come down to this.

There's a huge cheer rising up for the runners. Just another few minutes, and all that nervous energy will be let loose over 26.2 miles.

BBC One

Grab your remote! We're switching our TV coverage over to BBC One for the start of the mass race and the elite men. 

There is also commentary available on BBC Radio 5 live sports extra and BBC Radio London.

For some people, running a marathon just isn't enough - they want to break a world record at the same time.

There are 50 runners attempting to break a Guinness World Record in this year's marathon, and there's some interesting ones on the list.

• Liam White is attempting to run the fastest marathon dressed as an emoji (although we don't know which emoji yet - I'm hoping for the ghost)
• Fastest marathon in a sleeping bag? That's David Smith's target for today.
• Damian Thacker is making the 26 miles that extra bit difficult - by running it in Wellington boots

Go well, fellas! 

Image source, Getty Images

Ellie Thomason
BBC Sport at London Marathon

Some more pics from the start line - and two more runners attempting an official Guinness World Record today!

Image source, BBC Sport

It's almost time for the mass start - and of course, the elite men, to get underway - there's a real sense of excitement, and nerves, building around the start line now.

Steve Cram
BBC athletics commentator

Mary Keitany has gone off at a crazy pace - way too fast . She is usually a sensible athlete but she has gone off too quick today. 

Is she going to pay for this? Surely she will. 

Ellie Thomason
BBC Sport at London Marathon

I'm at the Green start line where Captain America  - also known as Barnaby - is aiming for three hours.

Image source, BBC Sport

Meanwhile in the women's race, Mary Keitany is still in the lead - but that bruising pace she set early on could be costing her.

She's still leading, though, while Alyson Dixonis heading up the British women. She's in 18th place overall, with Jo Pavey in 20th.