Jamaica's Usain Bolt easily outstripped American rival Justin Gatlin to claim his fourth consecutive world 200m title on Thursday and complete a rousing sprint double in Beijing.

Bolt clocked a world-leading 19.55 seconds to beat Gatlin by nearly two-tenths, thumbing his chest as he crossed the line to add the 200m to his 100m title at the world championships.

The clear victory extends Bolt's domination of sprinting which stretches back to when he took the world by storm at the 2008 Beijing Olympics, also at the Bird's Nest stadium.

Gatlin, who has served two doping bans and finished just one-hundredth of a second behind Bolt in Sunday's 100m, clocked 19.74sec, with South African Anaso Jobodwana taking bronze.

The victory meant Bolt has now remarkably won 11 of the last 12 individual Olympic and world sprint titles dating back to Beijing 2008, his only blip coming after a false start in the 100m at the 2011 worlds in Daegu.

"There was no doubt," said Bolt, who has had pelvic problems this season and did not consider an attempt on his own world record of 19.19sec, set in 2009.

"I knew I wasn't in the shape for a world record. But when it comes to the 200m, I am a different person, I was beaten there only once.

"My four world championships gold medals in the 200m, this is a big deal, a great accomplishment."

There was drama after the race, however, as a shoeless Bolt was downed by a cameraman on a Segway electric scooter who had strayed too close to the Jamaican.

The cameraman mounted a fixed railing and slipped backwards, shooting the Segway from under him into Bolt's heels and making the newly-minted champion fall backwards.
Bolt got up gingerly and limped away before continuing his victory lap.

Gatlin, meanwhile, said his age had showed in the race.

"I feel tired. Going through three 100s and three 200s is taxing on the body," he said.

"I'm the oldest person in the field and am still running and running pretty well. To be able to run 9.74sec is a really good showing.

"I gave it all I could give."