Walkers, long-distance swimmers and decathletes braved relentless rain in the Chinese capital on Thursday as the 13th day of the Olympics [Images] got under way.

- Vijender ensures third medal for India

Russia's [Images] Olga Kaniskina led from the start to win the first gold of the day in the women's 20km walk, and Maarten van der Weijden of the Netherlands timed his final burst perfectly to win the men's 10km marathon swim.

Playing on wet sand in front of a crowd draped in multi-colored plastic ponchos, China's Zhang Xi and Xue Chen took the bronze in the women's beach volleyball.

The semi-finals and finals of the men's and women's BMX competition were postponed until Friday after officials decided the dirt course was too dangerous.

The rain, though, failed to dampen the buzz around Jamaica's Usain "Lightning" Bolt, who was celebrating his 22nd birthday on Thursday after winning a second sprint gold and setting another world record the night before.

Bolt was again the toast of his Caribbean homeland with a blistering 200 meters win that broke American sprinter Michael Johnson's 1996 world record.

Added to his earlier 100m victory, that made Bolt the first man since America's Carl Lewis [Images] in 1984 to win the double and cemented Jamaica's reputation for speed as well as reggae.

"I'm number one," the joyous athlete mouthed at cameras, thumping his chest and blowing kisses at the 91,000 Bird's Nest crowd.

In a remarkable double disqualification, Americans Shawn Crawford and Walter Dix came fourth and fifth after Bolt but took silver and bronze when two athletes ahead were disqualified for running out of their lanes.

The Jamaican, variously dubbed the "U-Bolt" and "Insane Usain", may now return to the track and try for a third gold in the 4x100m men's relay on Friday.

JAMAICA, U.S. SHOWDOWN

Before then, the limelight turns to Jamaica's similarly high-achieving women in Thursday's 200m showdown.

Jamaican women have already swept the 100m medals.

The joint silver medalists from that race, Sherone Simpson and Kerron Stewart, plus defending champion Veronica Campbell-Brown, will lead the Jamaican charge in the 200m at 7:30 p.m. (1700 IST).

For the Americans, world champion Allyson Felix, Muna Lee and Marshevet Hooker are hoping to regain sprinting pride for the sport's traditional superpower.

Campbell-Brown was relishing the chance to bring more gold home. "Over the years, Jamaica is very strong, and I think everyone is just working very hard," she said.

Also looming on Thursday is the 110m hurdles final, which was shaping into one of the high points of the Games but is now deflated by the absence of Chinese favorite Liu Xiang.

The Olympic champion limped from the track injured, leaving Chinese fans in tears and clearing the way for Cuban world record-holder Dayron Robles. "I'm very calm. I'll win the gold medal," he said.

The Chinese can at least console themselves with a look at the gold medal table, where they have built up a seemingly unassailable lead of 45. The hosts' new sporting superpower status mirrors their growing global economic and political clout.

On a packed day of athletics, Americans Jeremy Wariner and LaShawn Merrit go head-to-head in the 400m on Thursday too.

The decathlon began with 100m and javelin rounds, with Czech world record holder and Olympic champion Roman Sebrle testing his battered body once again in athletics' most grueling event.

He was speared in the shoulder by a javelin in early 2007.