Concerns have been raised about the health hazards to tennis players competing in the China Open after one competitor complained of “uncontrollable” coughing as the air quality reached “hazardous” levels.

The tournament in China’s capital has been hit by smog, which on Wednesday cut visibility to just over half a mile and led China’s National Meteorological Centre to issue a yellow alert. According to the US Embassy in Beijing the conditions are “hazardous”.

World number 42 Martin Klizan on Monday posted a message on Facebook claiming the air pollution had caused him “uncontrollable” coughing during his first round defeat to Fabio Fognini. He also threatened not to play in Beijing again if the conditions didn’t improve. The Slovakian later removed the post.

Jo-Wilfried Tsonga, who also lost in the first round, had to be treated for dizziness and received on-court medial treatment, however the Frenchman refused to speculate on whether smog was at the root of his problems.

CNN quoted one spectator at the National Tennis Centre as saying: “There is definitely danger to the athletes.”

Novak Djokovic is the number one seed having never lost a match in Beijing, a record now covering 25 matches dating back to 2009. The five-time winner of the China Open beat Simone Bolelli in the first round. Rafael Nadal, Tomas Berdych and David Ferrer are also competing in Beijing.