Chinese swimmer Sun Yang won the men's 400m freestyle title at the National Summer Swimming Championships in Hefei after returning from a four-year ban for doping.

Sun, 32, was banned from competing for four years and three months for a dope test violation in 2018 in which he and members of his entourage smashed vials containing blood samples.

The ban, reduced from the original eight years on appeal, expired on May 28.

Sun missed national trials for the Paris Olympics because of the suspension.

On Sunday, the triple Olympic champion, representing Zhejiang province, won his race in a time of three minutes and 49.58 seconds.

"I could have done better," he told local media after the final.

"Four years away from competition, and without intensive training, I do feel rusty in controlling the tempo and I need more competitions.

"But it's a good start for my comeback and I'm happy with this result."

Sun, who also served a three-month suspension in 2014 for taking trimetazidine, which he said was to treat a heart condition, won Olympic gold in the 400m and 1500m freestyle in London 2012, then took the 200m title in Rio four years later.

The Chinese swimmer was certainly a polarising figure on the world stage, and was involved in a long-running and often acrimonious row with Australian rival Mack Horton.

The Aussie openly referred to Sun as a "drug cheat" and refused to share the podium at several high-profile meets.

China's swimming team was under intense scrutiny during the Olympic Games in Paris over the country's doping record.

The country secured 12 medals in swimming at the Games, including two golds.