Chinese swimmer Sun Yang's second gold medal at the 2019 world championships has been marred by another negative incident on the podium, clashing with Britain's Duncan Scott during the presentations of the men's 200-metre freestyle medallions.

Key points: Lithuanian Danas Rapsys was disqualified, bumping Sun Yang up to first place

Lithuanian Danas Rapsys was disqualified, bumping Sun Yang up to first place Duncan Scott, who finished equal third, congratulated the other place-getters but snubbed Sun

Duncan Scott, who finished equal third, congratulated the other place-getters but snubbed Sun It comes two days after Australian Mack Horton refused to shake hands with the Chinese swimmer

Sun was awarded the gold medal after Lithuanian Danas Rapsys, who finished first, was disqualified for moving on the blocks.

Scott, who finished joint third, refused to shake hands with Sun, in a show of further tension just days after Australian Mack Horton refused to share a podium with the Chinese swimmer over doping allegations.

During the 200-metre medal presentation, Scott congratulated silver medallist Katsuhiro Matsumoto of Japan and Russian Martin Malyutin, who finished in the same time as the Briton, but completely blanked Sun.

The Chinese swimmer reacted angrily, shouting and gesturing at Scott, with TV cameras capturing the Chinese champion saying "you loser, I am winning" to Scott.

Scott also refused to take part in a group photo on the podium and kept his distance from Sun as they left the stage.

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The incidents have prompted swimming's governing body FINA to issue more warning letters, both to Sun and Scott for "inadequate behaviour", following its warning of Horton for his podium snub.

Sun, who served a doping ban in 2014 and was labelled a "drug cheat" by Horton before the Rio Olympics final, got the green light to compete in the world championships in Gwangju after being cleared by a FINA panel of breaching the governing body's rules earlier this year.

However, the World Anti-Doping Agency is seeking to overturn the decision at the Court of Arbitration for Sport, leaving Sun's career hanging in the balance a year out from the Tokyo Olympics.

Sun, who also won gold in the 200-metre final in 2017, touched in a time of 1:44.93, with Matsumoto 0.29 behind in second and Malyutin and Scott taking bronze, 0.70 off Sun's time.

"My victory was because of my hard work. I continued to keep fighting, I didn't give up when I was in second place," Sun said.

"I was the only one to enter the [800-metre freestyle heats] this morning, so I was very tired. I just slept for an hour and a half this afternoon."

Sun Yang (right) shouted and gestured towards Duncan Scott following the medal ceremony. ( AP: Mark Schiefelbein )

Scott gave only a brief response to reporters when asked about the podium incident.

"You do quite a job of making sure everyone continues to know about it and so I guess that's all I have got to say about it," he said.

He said he was "Team Mack".

"If [Sun] can't respect our sport, then why should I respect him? Hopefully this will happen in more events," he said.

His teammate Adam Peaty, who swam in the 50-metre breaststroke semi-finals, said Scott was "completely right" to take action on the podium, adding that Sun should consider his place in swimming.

Peaty, who has previously criticised Sun and the decision to allow him to compete in Gwangju with the doping case hanging over him, said athletes had a right to speak out.

"I think the most important thing as a sportsperson is you have the right to a voice and Duncan showed his voice and so did the crowd," he said.

Sun Yang looked past Russia's Martin Malyutin towards Duncan Scott, shouting and gesturing. ( Reuters: Stefan Wermuth )

Sun was booed when he sat on his lane rope and celebrated his surprise 200m win as a shattered Rapsys left the pool.

"If people are booing him it's for a reason," Peaty said of Sun.

"He [Sun] should be asking himself now 'should I really be in this sport when people are booing me?'

"And if I was swimming [against Sun] I wouldn't even get on the podium for that matter."

The crowd at the Nambu University Municipal Aquatics Centre jeered the decision to disqualify Rapsys, who seemed to twitch on the starting blocks. The Lithuanian did not stop for questions after the race.

There was a mixed reaction to Scott's behaviour on the podium, with Chinese fans shouting and jeering while others cheered him as he left the pool deck.

Chinese social media has boiled over in recent days with angry reaction to Horton's snub.

One of the most widely shared images is of a statement translating to: "To be a decent person, don't be like Horton."

Horton refused to share the 400-metre freestyle podium with Sun on the opening night of the championships in South Korea.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 30 seconds 30 s Tensions were high as Mack Horton refused to stand next to Chinese swimmer Sun Yang

During the medal presentation, the 23-year-old Victorian stood behind the dais as Sun claimed the gold. Italy's Gabriele Detti picked up bronze.

Horton's silent protest later drew a warning from the sport's governing body.

In a statement, FINA said its executive group met in Gwangju to analyse the situation and decided to send a warning letter to Swimming Australia and Horton.

"While FINA respects the principle of freedom of speech, it has to be conducted in the right context," the statement read.

"As in all major sports organisations, our athletes and their entourages are aware of their responsibilities to respect FINA regulations and not use FINA events to make personal statements or gestures.

"The matter over which Mack Horton was allegedly protesting is currently under review by CAS and therefore it is not appropriate for FINA to prejudice this hearing by commenting further."

Australian swimmer Madeline Groves tweeted that it was "brave" for Scott to have spoken out given that Horton was issued a warning for similar behaviour.

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ABC/Reuters