Chinese swimming superstar Sun Yang stormed past his rivals to an emphatic 400 metres freestyle win on Tuesday as the Asian Games was rocked by its first positive drugs test.

The world and Olympic champion hit back from his shock 200m loss to Kosuke Hagino to dominate the Japanese and South Korea's Park Tae-Hwan, winning comfortably by 1.3 seconds.

Sun roared in celebration at the win, among six for China on the night as they finally hit form in the pool and leapt ahead of Japan 11-7 in the swimming titles tally.

It completed a triumphant day for Asia's powerhouse, which has long dominated the regional Olympics and has now accumulated 39 gold medals, more than double the 17 of second-placed South Korea.

There was controversy elsewhere after it emerged that a footballer from Tajikistan had become the first athlete at the Incheon Games to fail a doping test.

"It's a confirmed case," a source told AFP, adding that the as yet unidentified player would be kicked out of tournament.

The Central Asian republic are due to play Iraq in the second round of the men's football on Thursday.

The doping case comes after two incidents of alleged sexual assault at the Games, involving an Iranian football official and a member of the Palestinian team.

Sun, who blamed a thumb injury for his 200m loss to Hagino, strolled out for the race wearing a pair of gold headphones and he kept his cool when Hagino shot out to an early lead.

The towering Chinese reeled him in by the halfway mark and powered away over the second 200m to take Park's Asiad crown, as he did in the same event at the 2012 Olympics.

Olympic champion Ye Shiwen crushed the competition in the women's 400m medley, Ning Zetao won the men's 50m freestyle and Chen Xinyi won the women's 100m butterfly before China's women finished off with 4x200m freestyle gold.

Shooting sensation

China claimed 14 golds on day four across shooting, wushu, weightlifting, synchronised swimming and gymnastics, where Yao Jinnan won the women's individual all-round title.

Eighteen-year-old hooting sensation Yang Haoran led a sweep of the men's 10m air rifle event as the world champion claimed the individual title after helping China to team gold.

Teammate Cao Yifei picked up the silver, conceding the lead to Yang in the last two shots of a well-contested eight-man final.

Bronze went to Abhinav Bindra, India's first and only individual Olympic gold medallist who has announced he is retreating from full-time shooting.

"I have been shooting for the last 20 years -- there is nothing else I have done all these years -- and I know it's time to rethink my future," Bindra said.

Another rush of weightlifting records saw Taiwan's Lin Tzu-chi break two world bests to win the women's 63kg, while China's Lin Qingfeng took gold in the men's 69kg.

China's world and Olympic champion Lyu Xiaojun summoned up a glorious final lift, staggering to his haunches but then recovering with sheer determination to clean and jerk 200kg and win the men's 77kg.

In squash, celebrated women's world number one Nicol David fought back from a game down against fellow Malaysian Low Wee Wern to successfully defend her title.

China took on hosts South Korea in the men's team badminton final.