BEIJING (REUTERS/XINHUA) - China's world and Olympic swimming champion Sun Yang is almost back in shape ahead of this month's world championships, state media quoted his coach as saying.

"Sun is almost back to his peak. Judging from his training, he is about 90 or 95 percent of his peak form," said coach Zhang Yadong, according to the official Xinhua news agency.

The 23-year-old Sun is expected to compete in the 200, 400, 800 and 1,500 metres freestyle events at the meet in Kazan, Russia.

He said: "It will be a huge challenge for me. I'd rather keep the goal in my mind than speak it out.

"When I was little, I watched Michael Phelps compete in five or six events at a worlds, so I want to try it as well."

He is currently ranked in the world's top 10 in all four races, and within the top-five in three of them. Sun's 200m freestyle time of 1min 45.75sec this year is second only to Germany's world record holder Paul Biedermann's 1:45.60 set in April.

Sun has been caught up in a number of controversies in the past. He has a strained relationship with former coach Zhu Zhigen and was involved in a drunk driving scandal in 2013.

He had tested positive for a banned stimulant trimetazidine at the Chinese National Championships and was quietly given a three-month suspension in May 2014 that expired in time for Sun to compete and win gold in the 400 and 1,500m individual freestyles, and the 400 free relay at the Asian Games in Incheon later that year.

While Sun and fellow Olympic champion Ye Shiwen will be spearheading the team while 2012 London Olympic 200m butterfly champion Jiao Liuyang, and world champion Liu Zige, would miss the trip, Xinhua said.

Liu failed to make the cut while Jiao has been suffering from a stomach problem, the report added.

The swimming competition at the championships begins on Aug 2.