Usain Bolt has the potential to astound the world again after rewriting the men's 100 and 200 meters records over two epic seasons, four-times Olympic sprint champion Michael Johnson said Monday.

American Johnson reduced his own world 200 record by nearly a third of a second at the 1996 Atlanta Olympics to 19.32, a mark statisticians predicted would last for at least a quarter of a century.

It fell in less than half that time. In 2008, Bolt sliced Johnson's mark to 19.30 at the Beijing Olympics and he cut it further to 19.19 at the Berlin world championships the following year.

He's very, very young, still very, very raw, so there's certainly still room for improvement, amazing as that may seem for somebody who is running as fast as he is, Johnson told Reuters.

Johnson, speaking at the launch of a partnership between the Laureus Sport for Good foundation and Connie Henry's Track Academy in north London, said nobody could predict Bolt's limits.

The great thing about Usain Bolt is that he is testing those limits and that's what's exciting about what he is doing, making people rethink what they previously thought was possible, making people rethink what the human limit is, he said.

Johnson, the only man to win the Olympic 200-400 double, said he believed the Jamaican could also break the world 400 record he set at the 1999 Seville world championships.

I think he could, I don't think he wants to, he has said that he doesn't want do that type of training but he has the ability, he said.

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