American Dalilah Muhammad broke her own world record to win the women's 400 metres hurdles at the Athletics World Championship.

She crossed the line in a time of 52.16 seconds on Friday, edging out compatriot Sydney McLaughlin in a gripping race.

The 29-year-old Muhammad, the 2016 Olympic champion, crossed the finish line 0.04 seconds faster than her previous world record set in July.

The American attributed her two world marks to her work ethic, and said she was focused on successfully defending her title at next year's Tokyo Olympics.

"It's just how I work," she told reporters after the race. "I go out there every day and just try to give it my all. It feels good to have it come when it matters."

Muhammad was only slightly ahead of silver medallist McLaughlin over the first 100m of the race, but her lead grew as they came through the second bend.

When she crossed the finish line, Muhammad had no idea she had set a new record.

"I didn't even know who had won the race," she said.

Barshim celebrates on the landing mat after his winning jump

Lifted by a packed stadium, Qatar's Mutaz Barshim soared to victory in the men's high jump to give the hosts a long-awaited first gold medal.

With the crowd on their feet for every jump, Barshim delivered the performance they demanded by clearing 2.37 metres on his first attempt before watching on as his rivals failed to match his effort.

Two Russians, who are in Qatar competing as neutral athletes, completed the podium with Mikhail Akimenko taking the silver and Ilya Ivanyuk the bronze.

Barshim becomes the first man to successfully defend the world high jump crown.

Qatar's big night, however, ended on a sour note when technical issues prevented the awarding of the high jump medals and the athletes were left standing at the side of podium as officials scrambled to fix the problems.

In the end, with the stadium having emptied the athletes walked off the stage without a ceremony taking place and Officials later announced that the medal presentation would take place on Saturday.

Kenya's Conseslus Kipruto beat Lamecha Girma of Ethiopia in a photo finish to successfully defend his 3,000 metres steeplechase title.

In the home straight the race came down to a 100m sprint and Kipruto just won it, dipping to edge out the 18-year-old Girma on the line in a winning time of eight minutes, 1.35 seconds.

Girma was 0.001 seconds back and had to settle for silver, Ethiopia's first ever medal in the event.

Morocco's Soufiane El Bakkali completed the podium by taking the bronze.