Sun Haiping (R), coach of China's Liu Xiang, cries during a news conference with China athletics team's head coach Feng Shuyong at the National Stadium during the Beijing 2008 Olympic Games August 18, 2008. [Agencies]

The son of a Shanghai truck driver, Liu became a national hero overnight when he matched the then world record to win Olympic gold in Athens in 12.91 seconds four years ago.

After a 2005 season where he struggled with injury and only managed a silver behind France's Ladji Doucoure at the world championships, he stormed back in 2006 to set a world record of 12.88 in Lausanne.

Victory in Osaka last year gave him his first world title and further ramped up the expectation that he would win gold again in Beijing.

Chinese fans were left in shock but most were sympathetic towards Liu.

"It must hurt, we can see he has impression of pain in his face," said Tracy Yang, a Tsinghua University student. "We support him, he will be back."

Cuba's Dayron Robles, who qualified from his heat on Monday morning, took Liu's world record with a run of 12.87 seconds in June.

Liu's preparations for the Games were disrupted by a hamstring injury which forced him to withdraw from a meeting in New York on May 31 and he had not competed in public for more than two months.