Nathan Chen won a dominant figure skating gold for his first Olympic title with reigning champion Yuzuru Hanyu falling twice on the ice and failing to win a medal in Beijing on Thursday.

One of the most eagerly anticipated events of the Games came as the IOC refused to comment on a reported doping case involving another figure skater, 15-year-old Russian sensation Kamila Valieva.

Eight golds were up for grabs on the sixth day of competition in the Chinese capital, with the Americans Chen and Chloe Kim, in snowboard halfpipe, blitzing the opposition to win two of them in style.

An Olympic title had been the only major prize eluding three-time world champion Chen, but he finally won the gold with an overall score of 332.60, while the Japanese duo of Yuma Kagiyama, on 310.05, and Uno Shoma took silver and bronze. Hanyu was fourth.

Kamila Valieva led Russia to team gold in Beijing
Kamila Valieva led Russia to team gold in Beijing AFP / SEBASTIEN BOZON

An elated Chen said: "I'd always of course dreamed about making the Olympics and winning the Olympics but I was like... I don't know if I can make that happen.

"I haven't really had time to process fully but it's amazing so far."

Hanyu was chasing a third Olympic gold but having started the day eighth after a disappointing short programme, the Japanese icon went for broke with a free skate that included an attempt at a quadruple axel -- something no skater has ever landed in competition.

That remains the case after the "Ice Prince" tumbled twice, once trying to nail the notoriously difficult jump.

Chloe Kim retained snowboard halfpipe gold in style
Chloe Kim retained snowboard halfpipe gold in style AFP / Ben STANSALL

"Honestly, it feels like everything has gone wrong this time around, but I did my best," said the 27-year-old Japanese skater, who only arrived in Beijing on Sunday.

Skating to "Rocket Man" by Elton John, Chen lived up to his nickname "Quad King" in a routine in which the 22-year-old landed five quadruple jumps, to rapturous cheers from the crowd.

After the US won their first gold in Beijing with snowboarder Lindsey Jacobellis on Wednesday, they now have two more in quick succession.

The 21-year-old snowboard sensation Kim had the halfpipe title in the bag after only the first of three runs, scoring a whopping 94.00 points to give her a virtually unassailable lead.

Yuzuru Hanyu finished down in fourth in the figure skating
Yuzuru Hanyu finished down in fourth in the figure skating AFP / SEBASTIEN BOZON

She clutched her helmet and fell to her knees after sliding into the finish area, then got back up and turned the rest of the competition into her own private victory lap.

She fell on her second run and received a hug from Californian-born Chinese freestyle skiing star Eileen Gu, who was watching at the finish area, before making her way back up the hill for her third and final attempt.

By then she already had the title wrapped up, and although she fell again on her final run, Kim celebrated with the other riders when she slid into the finish area.

Kim became the youngest woman to win an Olympic snowboarding medal when she won halfpipe gold as a 17-year-old at the 2018 Pyeongchang Games.

Kamila Valieva led Russia to team gold in Beijing
Kamila Valieva led Russia to team gold in Beijing AFP / SEBASTIEN BOZON

She took a two-year break from competition after her Olympic success as she struggled to cope with the pressures of fame.

"What you guys need to understand is that this isn't an easy sport," she told reporters on Thursday.

"It's all about being smart with it, prioritising my health and just taking it step by step. We'll go from there."

But the action on the snow and ice was overshadowed after Russian media reported that 15-year-old figure skating star Valieva, who led Russia to team gold at the Games this week, tested positive for a banned heart medication before the Olympics.

The positive test could cost Russia the team gold and also threatens Valieva's participation in the individual event that starts on Tuesday.

Russian athletes are competing in the Beijing Games as the Russian Olympic Committee (ROC) after the country was banned because of a massive state-sponsored doping scheme at the 2014 Sochi Olympics.

The sample in question was obtained before Valieva won the European championship last month, the RBC newspaper reported late Wednesday.

The drug detected is trimetazidine, a metabolic agent that is prescribed for the treatment of angina and vertigo, according to Kommersant newspaper.

It is banned by the World Anti-Doping Agency because it can increase blood flow efficiency and help endurance.

The reports said the test result was the reason that the team medals ceremony was removed from its scheduled slot on Tuesday.

The Russians won the gold medal in the team competition with the United States taking silver and Japan bronze, but the ceremony did not take place as planned.

International Olympic Committee spokesman Mark Adams said on Thursday an "active legal case" was under way concerning the medal ceremony and so he could not comment on the reports.

He said claims that the case concerned doping were "speculation".

"We had a situation arise yesterday that has all sorts of implications," he added.