Usain Bolt, the Jamaican world 100m record holder, beat Asafa Powell, his closest rival, to qualify for the Olympics but refused to confirm he will run in Beijing.

Bolt clocked 9.85 seconds to Powell's 9.97 seconds, with Michael Frater claiming the third spot for the Games in 10.04.

However, Veronica Campbell failed to qualify for China after finishing fourth. The world champion ran a season's best 10.88 secs, but was beaten by Kerron Stewart (10.80secs), Shelly-Ann Fraser (10.85secs) and Sherone Simpson (10.87secs)

Glen Mills, Bolt's coach, said they would wait until August before deciding on whether he would double up in the 100m and 200m and become only the ninth man to achieve the feat at the Olympics.

Bolt beat Powell's existing world record down to 9.72 secs in New York on May 31, but the 21-year-old sees the 200m as his stronger event.

"We will not decide until August, when we have to let the Jamaica Amateur Athletic Association know," Mills said. "We still have to assess how he does in the 200m.

"The problem is that when we started the season, our plan was to run the 200m only. We have to be careful how we see-saw with that plan. So we are taking it very seriously. We are not going to be rushed into making a firm decision."

Meanwhile, Tyson Gay, the American world champion, ran the fourth fastest time ever (9.77secs) at the American trials. Gay is yet to qualify for the Olympics despite his personal best time as it came in the quarter-finals. The top three Americans from Sunday's final will be selected to represent the US in Beijing.