Olympic champions Zhang Yufei and Wang Shun powered to gold on Sunday as hosts China won all seven races on the opening night of swimming at the Asian Games, smashing a slew of Asian records.

Zhang successfully defended her 200m butterfly crown, cruising to victory in Hangzhou ahead of Chinese teammate Yu Liyan in a new Games-record time of 2min 05.57sec.

That time has been bettered this year only by Canadian star Summer McIntosh and Australia's Lizzie Dekkers, as Zhang builds towards defending her Olympic title in Paris next summer.

"I felt I could have gone even faster," she warned. 

"My first mission was to take the gold for China. Next was to beat Jiao Liuyang's Games record, and I also did that. I actually felt the pool was a little slow for me and I told my coach that I wasn't feeling in good form." 

Fresh from beating a stacked field to win the 100m world title in Fukuoka in July, the dominant 25-year-old was a body-length clear after the first 50m and never threatened.

Yu (2:08.31) bagged silver and Japan's Hiroko Makino (2:09.22) took bronze.

Triple breaststroke world champion Qin Haiyang had upstaged Wang in the morning heats of the 200m medley, but his Chinese teammate saved his best for last, blitzing to a new Asian record of 1:54.62, the fastest in the world this year.

Wang powered through the opening butterfly and backstroke legs to give himself a handy buffer heading into the breaststroke and Qin couldn't catch up.

- Confidence-booster -

It was a welcome return to form for Wang, who had faltered since stunning Britain's Duncan Scott to take Olympic gold, missing out on the final at the last two world championships.

"I gave it my all today. I'm very happy and emotional to have won the event. It exceeded my expectations," he said.

"I didn't do very well at the world championships, so to be able to recover here is something I'm very pleased with. This is a confidence-booster for me."

Qin, who burst onto the scene at the July world championships, becoming the first man in history to sweep all three breaststroke titles, settled for silver in 1:57.41 with Japan's 2019 world champion Daiya Seto third.

Both China and Japan claimed 19 golds at the Asian Games in 2018, but the hosts are favourites to top the medals table on home turf after winning all seven races on Sunday.

Japan are in disarray after an awful world championships, finishing 17th with just two bronze and long-time head coach Norimasa Hirai bowing out.

In contrast, China came third behind big guns Australia and the United States after claiming five gold, three silver and eight bronze.

In other races, China's Pan Zhanle got the better of South Korean star Hwang Sun-woo to win the 100m freestyle gold.

Pan powered to the wall in a new Asian best 46.97sec to beat teammate Wang Haoyu (48.02) with Hwang having to settle for bronze in 48.04.

Tang Qianting, who set a new Asian best in the heats, clocked 29.96 to win the women's 50m breaststroke while two-time world champion Xu Jiayu defended his 100m backstroke title in a new Asiad record 52.23.

Li Bingjie added another gold to the Chinese haul by winning the women's 1500m freestyle, outlasting teammate Gao Weizhong in a gruelling 15min 51.18sec, another Games record. 

The hosts, led by Zhang Yufei, rounded off a dominant night by winning the women's 4x100m freestyle in a new Games record 3:33.96.

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