Sun Yang of China celebrates his win after men's 200m freestyle final in Rio de Janeiro, Brazil, August 8, 2016. [Photo/Xinhua]

China's Sun Yang has vowed to come back stronger after his surprise elimination from the men's 1,500m freestyle at the Rio Games on Friday.

Sun, the gold medallist in the event in London four years ago, clocked 15 minutes 1.97 seconds in his heat on Friday.

It was over half a minute slower than the world record he achieved at the London Games and more than 17 seconds off the pace set by Italy's Gregorio Paltrinieri here.

Sun said he was struck down by illness after winning the 200m freestyle gold medal on Monday.

"I was quite sick right after the 200m," Sun said. "I didn't think my body condition had declined that much after the 200m but I swam one minute, 44 seconds for the 200, something I'd never done before, and that was really intense. I think it influenced my body condition too."

Sun said his failure to make Saturday's 1,500m final would drive him to work harder and cited US swimming legend Michael Phelps as a source of inspiration.

"I'm looking forward to competing in more 1,500m events when I'm training in the US or Australia," the 24-year-old said. "I'll try to start finding the rhythm again because the key is in rhythm control.

"There's another major competition in China (in Huangshan) in September. Originally I was thinking about not going because the past year has been quite hard for me. Now I'm actually thinking about competing in Huangshan in multiple events."

"Actually, I think it is amazing and unbelievable what Phelps has done. His persistence actually encouraged me to work harder and be more strict about my training because every athlete would love to take it a little bit easier in training.

"Phelps has set a great model for me to keep me motivated."