RIO DE JANEIRO (AFP) - China's Sun Yang, the reigning Olympic champion and world record-holder, failed to qualify Friday (Aug 12) for the final of the 1,500m freestyle at the Rio Games.

Sun lurked just off the pace in his heat until fading to seventh at the 800m mark and laboured home in 15min 01.97sec, seventh in a heat won by American Jordan Wilimovsky in 14:48.23.

He was 16th-fastest overall, 17.46sec behind top qualifier Gregorio Paltrinieri (14:44.51).

Sun departs Rio with a gold in the 200m freestyle, but settled for silver behind Australia's Mack Horton in his defence of the 400m free title he won in London.

His doping past was also put under the microscope when Horton called him out as a "drug cheat" over Sun's three-month suspension in 2014 for a banned stimulant.

It was another blow for China at the Olympic Aquatic Stadium, where they have been unable to reproduce the five-gold haul that saw them second to the US in the swimming medals table in 2012.

Sun's 200m free triumph was their only gold over the first six days of competition.

China's two silvers include Sun's runner-up finish to Horton. They also have three bronze, and have swimmers in two of the four individual finals later on Friday.

Worse, China's Chen Xinyi was suspended after failing a drugs test.

The Court of Arbitration for Sport said the 18-year-old was "provisionally suspended from competing at the Olympic Games in Rio 2016" after failing a test for a diuretic after finishing fourth in the 100m butterfly on Sunday.

She was scratched Friday morning from the heats of the 50m freestyle, with CAS saying a final decision on her case would be made "before the end of the Games".