Triple Olympic champion Jamaican Usain Bolt cruised into the second round of the 200 metres at the world championships on Tuesday, 36 hours after shattering the 100m world record to win gold.

On a chilly and windy morning, Bolt looked a bit stiff round the bend but was still in command of his heat, winning in 20.70 seconds.

"I'm feeling alright, a little bit tired, but nothing a good night's rest won't cure," the 22-year-old told reporters.

With 2007 champion Tyson Gay out with a groin injury that flared up following his defeat to Bolt in the shorter sprint, the Jamaican world record holder is the overwhelming favourite to win the title on Thursday.

American Shawn Crawford, silver medallist behind Bolt in the Olympics last year, clocked the best overall time of 20.60 to ease into the second round.

"I did what I was supposed to do. I tried to get as many cobwebs out as I could," Crawford told reporters.

Compatriot Wallace Spearmon, who initially had won bronze in the Beijing Games only to be disqualified after stepping out of his lane, joined him with a run of 20.66.

Apart from Bolt, Spearmon is the only other runner in the field to have cracked the 20 second mark this season.

World champion Kerron Clement clocked the year's best time to retain his 400 metres hurdles title on Tuesday.

The American, runner-up at the 2008 Beijing Olympics, recovered from hitting the first hurdle to grab the lead on the back straight and power to victory in 47.91 seconds, ahead of Puerto Rican Javier Culson who caught 2005 champion Bershawn Jackson at the finish.

Felix Sanchez, world champion in 2001 and 2003, was last in 50.11.

Sanya Richards won the world championship women's 400 metres in convincing style.

Richards, third in Beijing after going into the 2008 Olympics as favourite, has been the form one-lapper this season and kept her discipline after Russian Antonina Krivoshapka had started strongly.

The American took control coming into the final bend to win in 40.00 seconds, holding off Jamaica's Olympic silver medallist Shericka Williams (49.32) with Krivoshapka third.

"It's better than good," Richards said.

"I'm overwhelmed and excited to be finally standing top of the podium.

"Finally the work has paid off. It's the best feeling in the world."

Steffi Nerius nearly lifted the roof off the Olympic Stadium when the 37-year-old German won the javelin.

It was a familiar story for Nerius, who picked the perfect time and place to end her run of three successive world bronzes.

Her opening throw of 67.30 metres did the damage and Olympic and defending champion and world record holder Barbora Spotakova of the Czech Republic could manage only 66.42 in response for silver.

Maria Abakumova of Russia took the bronze (66.06m).

Nerius, who took Olympic silver in 2004 and bronze from the 2003, 2005 and 2007 world championships, set her marker out from the start with what turned out to be the winning effort.

Ezekiel Kemboi broke clear in a frantic last lap to clinch the men's 3,000 metres steeplechase world championship gold medal on Tuesday and extend Kenya's rule in the event.

Compatriot Richard Kipkemboi Mateelong took silver with fast-finishing Frenchman Bouabdellah Tahri preventing a Kenyan clean sweep by pipping Paul Koech on the line for bronze.

Athens 2004 Olympics champion Kemboi, the only runner to crack the eight-minute mark this year, broke from a four-man pack 300 metres from the finish and held on to win in 8:00.43, a championship record.

Kenyan-born athletes have won the last 10 men's steeplechase world titles, though Stephen Cherono changed his name and nationality to win in 2003 and 2005 as Saif Saaeed Shaheen of Qatar, and also the last seven Olympic crowns.

Kemboi finished second in the previous three editions but finally took gold.

Briton Phillips Idowu produced a lifetime best of 17.73 metres to win the men's triple jump.

Idowu took gold with a leap of 17.73 metres to win the triple jump and leave defending world and Olympic champion Nelson Evora of Portugal second on 17.55.

British woes were eased a little when Idowu, the 30-year-old Olympic silver medalist, landed in the sand pit at 17.73 metres - the best in the world this season - while Evora (17.55) was second and Alexis Copello of Cuba (17.36) was third.