While the colour-changing Water Cube building has figured large in the first half of the Games, attention is now also firmly on the equally futuristic Bird's Nest athletics venue.

Tyson Gay of the US (R) runs next to Olusoji Fasuba of Nigeria in the men's 100m heat during the athletics competition of the Beijing 2008 Olympic Games at the National Stadium, August 15, 2008. [Agencies]

The Games' blue riband track race, the 100m sprint, takes place in the evening in front of more than 90,000 people, and millions worldwide, in the Bird's Nest stadium.

It looks like a fascinating three-man, two-nation affair.

Jamaica's Usain Bolt seemed in superb form in the heats on Saturday, having time to look around and still win his second round race in the day's best time of 9.92 seconds.

Bolt has burst on to the 100m scene in the last year, shouldering aside American world champion Tyson Gay and fellow Jamaican former world record holder Asafa Powell.

Formerly a 200m specialist, Bolt set a new world best of 9.72 in the 100m in May. He hopes to be the first man to complete the 100m and 200m Olympic double since American Carl Lewis in 1984.

A new world record looks feasible, given the tall 21-year-old appeared to have so much to spare on Friday. "I looked around to make sure I was safe and I shut it off," he said.

Despite its tradition of producing world class sprinters, Jamaica has yet to win a men's 100m gold and the islanders will be watching tensely at 10.30 pm (1430 GMT).

Powell complained of stomach ache but comfortably won his second heat on Saturday in 10.02 and is still in the hunt for a first global title.

Gay took gold in both the 100m and 200m at the world championships last year but a hamstring injury is restricting him to just the 100m in Beijing.