Perfect from Tiffany Porter, who wins the race and the Briton is into the final, which comes up later at 14:35 BST.

Cindy Ofili is cheering and applauding from the sidelines. A job well done from Porter.

The gun goes but it is a false start from American Kendra Harrison. She stands there waiting for confirmation. And the dreaded red and black card comes out. She is gone. Off goes Harrison, muttering to an official.

She doesn't seem to think she's done anything wrong but she was definitely the first to move. She also didn't know what the black and red card meant. But it means the end of her hopes.

A terrible few minutes for American sprint hurdlers.

So little sister has had her go, and now it is her big sister, Tiffany Porter, who aims to book her place in the final.

Image source, Getty Images

Steve Backley
Four-time European javelin champion on BBC TV

Not the start Goldie Sayers is after in the women's javelin qualification. She records a throw of 58.11m with her second throw after 58.28m with her first attempt. She needs a better third round or is heading home early.

Image source, BBC Sport

This is how Dawn Harper-Nelson's medal hopes ended in dramatic style.

Image source, BBC Sport

Ouch. American Dawn Harper-Nelson crashes into one of the hurdles. She was the second fastest in the field. She was tipped as a medal contender but hits the second hurdle hard with her trailing leg and that sends her face-first into the next hurdle.

Britain's Cindy Ofili, running in lane nine, finishes sixth in 12.91 seconds. It won't be enough for a place in the final.

Great Britain's Cindy Ofili is in the first semi-final in the women's 100m hurdles. America's Sharika Nelvis looks the woman to beat, after she recorded a time of 12:34 seconds earlier this year.

Great Britain have won three medals so far in this World Championships, but we want your predictions on how many medals hey will have by the end of the day.

Will it remain at three or will a British athlete or two be celebrating later? Vote now on the right-hand side of this page and voting will close at 13:00 BST.

Great Britain will be represented in the women's 100m hurdles semi-finals on Friday by sisters Tiffany Porter and Cindy Ofili.

Porter, a bronze medallist at the World Championships in 2013, raced to a comfortable victory in her heat, in a time of 12.73 seconds.

Her younger sister, Ofili, finished fourth in her heat, in 12.97, to also progress to the semi-finals.

Image source, AFP/Getty

Not the best of start for Great Britain's Goldie Sayers as she throws 58.28m, well short of the qualifying distance of 63.50m.

Still two more attempts for the 33-year-old, who has a good deal of strapping around her right knee.

Steve Backley
Four-time European javelin champion on BBC TV

We mentioned that Robbie Grabarz had not made it into the high jump final.

"It was not to be for Robbie Grabarz. But he recently went for knee surgery and the surgeon couldn't believe he walked in as his knee had been so bad. Hopefully he will have gained something from competing here."

iamsusannkala:  Seeing the #SouthAfrican, external flag flying alongside USA & Jamaica. Well deserved bronze for #Jobodwana, external well done!  

Ianthompson:  Dina will need to take lumps out of Kathy Cook's record to win. Schippers walked the last 25m of her semi. Have a blast, Dina!  

The first medals of the day have already been handed out. And China claimed a one-two finish in the 20km walk to win their first gold medal of the World Championships.

Liu Hong and Lu Xiuzhi entered the Bird's Nest stadium side by side at the end of the race.

But it was world record holder Liu who took gold in 1 hour 27 minutes 45 seconds, with Lu a stride behind. Lyudmyla Olyanovska of Ukraine won the bronze medal, 28 seconds behind the Chinese walkers.     

Image source, Getty Images

Thirty-eight centimetres. That was all that separated Goldie Sayers from an Olympic Games bronze medal.

The Bird's Nest stadium in Beijing was the scene when Sayers finished fourth in the women's javelin final in 2008. Her best throw was 65.75m, agonisingly short of the 66.13m effort from Christina Obergfoll that won a bronze.

But can the 33-year-old Sayers book her place in the final? The first section in the javelin qualification has just started and we will be bringing you regular updates. She needs 63.50m to qualify for the final.

Image source, Getty Images

It has been a bad summer for Australian bowler Mitchel Starc, after losing the Ashes to England.

Image source, Getty Images

But his brother Brandon is having a happier time in Beijing, where the younger of the Starc siblings has qualified for the final of the high jump in a personal best of 2.31m.

Wonder if he is as handy with a cricket ball?

Image source, Getty Images

Image source, Getty Images

Earlier today, Great Britain's Robbie Grabarz failed to reach the final of the men's high jump.

Needing 2.31m for automatic qualification, the Olympic bronze medallist could only manage 2.26m.

Grabarz, who only returned from knee surgery this year, said: "I’m just happy to be here, I shouldn’t be saying that – but I am. 

"Surgery was just a year ago, and my body feels great – I just need to get technically fit, which shouldn’t be too difficult."

Olympic champion Ivan Ukhov also failed to qualify.

A touching / bizarre moment at the end of Usain Bolt's medal ceremony.

The photographer who crashed into him after the 200m final yesterday is waiting for Bolt so he can give the Jamaican a present, apologise for the incident and wrap what appears to be some kind of friendship bracelet around his wrist.

Bolt looks a bit bemused, but the pair shake hands and are friends, apparently.

Image source, BBC Sport