British skateboarding sensation Sky Brown, 13, qualified second for the women's park final as she bids to become the youngest gold medallist in Olympic history on Wednesday.

Brown was flawless in the three runs of her heat to register a best score of 57.40, trailing 15-year-old Japanese Misugu Okamoto (58.51) into the final at Tokyo's sun-baked Ariake Urban Sports Park.

Japan's Kokona Hiraki placed third in the heats among an ultra-young field where only eight of the 20 competitors were out of their teens.

Both Brown, at 13 years and 28 days, and Hiraki (12 years and 343 days) can become the youngest Olympic gold medallist, breaking the record of American diver Marjorie Gestring, who won 3m springboard gold aged 13 years and 268 days at the Berlin 1936 Games. 

Brown, Britain's youngest-ever Olympian, is competing just over a year after a horrific fall in training left her with skull fractures and a broken wrist and hand.

The accident would have ruled Brown, just 11 at the time, out of the 2020 Olympics if they had not been postponed for a year over the coronavirus pandemic.

Brown, born to a Japanese mother and a British father, opted to compete for Britain in 2019, preferring the more relaxed approach of the British team.

"I chose to compete for Britain because they told me 'Have fun, there's no pressure!'" Brown, then 10, said at the time.

Japan have won three of the six medals so far in skateboarding, which is making its debut as an Olympic sport as organisers try to reach new audiences.

Japan's Yosozumi wins skateboarding gold

Japan's Sakura Yosozumi won the women's park competition on Wednesday to maintain the hosts' stranglehold on Olympic skateboarding and stop Kokona Hiraki and Sky Brown becoming the Games' youngest-ever gold medallists.

The 19-year-old carved up the Ariake Urban Sports Park with a flowing opening run in the final and her 60.09 points proved enough for victory ahead of teammate Hiraki, 12, and Brown, 13.

Britain's Brown threatened to snatch a shock win with a flawless closing routine but her 56.47 was not enough. 

World number one Misugu Okamoto missed a medal when she fell on all three runs in the final to finish fourth.

Japan also snapped up the men's and women's street titles and they have now bagged five of the nine medals so far as skateboarding makes its debut as one of four new Olympic sports.

Both Brown, at 13 years and 28 days, and Hiraki (12 years and 343 days) were bidding to break an 85-year-old record to become the youngest Olympic gold medallists.

They had a shot at bettering American diver Marjorie Gestring, who won 3m springboard gold aged 13 years and 268 days at the 1936 Games in Berlin.

McLaughlin storms to gold and world record
Sydney McLaughlin obliterated her own world record to claim a thrilling last-gasp victory over rival Dalilah Muhammad in the Olympic women's 400m hurdles final on Wednesday.

In another classic duel between the two dominant American hurdlers, McLaughlin surged past Muhammad just metres from the line to win in 51.46sec, slicing a whopping 0.44sec off her previous mark of 51.90sec set at the US trials in June.

Muhammad, the 2016 Olympic and world champion, took silver with a time of 51.58sec, well inside the old world record, with Femke Bol of the Netherlands earning bronze in 52.03sec.

"What a great race," said McLaughlin. "I'm just grateful to be out here celebrating that extraordinary race and representing my country."

It was another epic world record-breaking battle between the 21-year-old McLaughlin and the 31-year-old Muhammad.

Muhammad set a world record when she won the US trials in 2019 ahead of McLaughlin, before again beating her for gold at the 2019 World Championships in Doha in a near photo-finish with a new record.

McLaughlin avenged that loss in Oregon in June to defeat Muhammad at US trials with a devastating world record run.

McLaughlin's victory on Wednesday came after a superb tactical race which saw Muhammad make a flying start in the lane outside her rival.

Muhammad led coming off the final hurdle but McLaughlin produced a late burst of speed to claim her first gold medal.

"I saw Dalilah ahead of me with one to go. I just thought 'Run your race'," McLaughlin said.

"The race doesn't really start until hurdle seven. I just wanted to go out there and give it everything I had.

"It's just about trusting your training, trusting your coach, and that will get you all the way round the track."

The win came a day after the men's 400m hurdles race produced an epic duel between Karsten Warholm and Rai Benjamin, which ended with Norway's Warholm also setting a world record.

"I can't really get it straight in my head yet. I'm sure I'll process it and celebrate later," McLaughlin said of her record run.

McLaughlin's world record on Wednesday is just the latest in a slew of records that have tumbled on the Olympic Stadium track, which athletes at the Games have said is conducive to fast times.

- Lyles eyes gold -
McLaughlin's hurdles gold was the first of five medals to be handed out on Wednesday.

The highlight of the evening session will come in the men's 200 metres, where the USA's Noah Lyles will aim to make up for a blunder which almost cost the reigning world champion and favourite a place in the final.

Lyles only qualified for the final as one of the fastest semi-final losers on Tuesday after inexplicably pulling up at the line in his semi-final.

That allowed him to be overtaken by Canada's Aaron Brown and Liberia's Joseph Fahnbulleh.

"I'm glad I made it to the finals and that is all that matters," a relieved Lyles said afterwards.

"I knew I was going to make it. It was a bit risky, I wouldn't lie, but I made it."

Other medals up for grabs on Wednesday include the men's 800m final, the women's 3,000m steeplechase and the men's hammer.

Wednesday also saw the start of the decathlon and heptathlon multi-discipline events.

Britain's Katarina Johnson-Thompson is looking to add Olympic gold to her 2019 world championship victory, while Canada's Damian Warner and French world champion Kevin Mayer battle it out in the decathlon.

Transgender lifter retires after Olympic debut

Transgender weightlifter Laurel Hubbard has announced she will retire in the wake of her groundbreaking appearance at the Tokyo Olympics this week.

The New Zealander on Monday contested the +87kg category weightlifting, in a debut the International Olympic Committee (IOC) described as the first appearance by an openly transgender woman at an Olympics.

While her appearance on sport's biggest stage was short-lived -- an "overwhelmed" Hubbard failed to complete a successful lift -- it was hailed by trans activists as a historic occasion for a marginalised community.

It also sparked a firestorm of debate about transgender participation in women's sport.

The intensely private Hubbard said she was now ready to step away from the spotlight.

"Age has caught up with me. In fact if we're being honest it probably caught up with me some time ago," said Hubbard, who at 43 was more than 20 years older than most of her rivals.

"My involvement in sport is probably due, if nothing else, to heroic amounts of anti-inflammatories, and it's probably time for me to start thinking about hanging up the boots and concentrating on other things in my life."

Hubbard praised the IOC for showing "moral leadership" in adopting inclusive polices that allowed her to participate at the Games. 

"I'm not sure that a role model is something I could ever aspire to be, instead I hope that just by being I can provide some sense of encouragement," she told reporters.

Critics argue athletes such as Hubbard, who was born male and transitioned to female in her 30s, have physical benefits hardwired into their bodies during their formative years.

These include greater muscle mass and lung capacity, leading to fears that female-born athletes could be forced to compete on an uneven playing field.

The IOC, under guidelines adopted in 2003, only allowed transgender participation for athletes who had undergone gender reassignment surgery but dropped the requirement in 2015, instead focusing on lower testosterone levels.

The governing body is set to release new guidelines on the issue after the Tokyo Games are completed.

Hubbard said she welcomed the discussion about the issues her debut had highlighted.

"I'm certain that a conversation needs to be had," she said.

"Although we have rules at the moment, they will no doubt change and evolve as more is known about transgender athletes and what that means for participation in sport."

Brazil's Cunha wins gold in marathon swim

Brazil's Marcela Ana Cunha said she had to be "cold mentally" to see off the challenge of defending champion Sharon van Rouwendaal on her way to Olympic gold in the women's 10-kilometre marathon swim on Wednesday.

Cunha won by less than a second from a fast-charging Van Rouwendaal in their early morning duel in Tokyo, timing 1hr 59min 30.8sec to 1:59:31.7 for the Dutch swimmer.

Kareena Lee took the bronze medal for Australia.

Cunha, 29, finished 10th in the event at the Rio Olympics and fifth at the Beijing Games in 2008.

The Brazilian said she had arrived in Japan desperate to win gold.

"We arrived here wanting, as much as you can, this medal and around 10 days ago, I said to my coach to win this race will be very difficult for my opponents because I want it so hard, so much and I'm really well prepared," she said.

"We had to be cool or 'cold' as Europeans (are)," she added. "We are Latin people -- we are hot, we are emotional people -- so I had to be very cold mentally in the race to be focused and I had to win it myself. I knew I was prepared for that."