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Bolt, whose father says owes his speed and power to the local yam vegetable, charged to a world record time of 19.30 seconds, falling to the floor in joy at the end.'I'm Number One,' he mouthed at TV cameras, beating his chest and blowing kisses at the 91,000 crowd in the Bird's Nest.
Bolt had won the 100m at the showcase Olympic stadium in swashbuckling style at the weekend, also setting a world record.
This time, he again joked on his way to the block, firing an imaginary arrow in the air, but looked deadly serious as he opened up a big gap and steamed through the finishing line to beat Michael Johnson's 1996 record by two hundredths of a second.
Dubbing Bolt 'Superman 2', Johnson -- commentating on the race for the BBC -- said: 'I looked at his start and just went, 'Wow'. Guys that tall should not be able to start like that ... He used every ounce of energy, he wanted that record.'
Nine men have now won the double sprint in Olympic history.
Bolt, who turns 22 on Thursday, has established himself as the joint hero of the Games along with American swimmer Michael Phelps who took an unprecedented eight golds.
Just as Phelps's exploits in the Water Cube, passing Mark Spitz's 1972 Munich record, have thrilled Americans, so Bolt has swelled national pride across his Caribbean homeland.
The lanky runner started sprinting only when a school cricket coach noticed his speed as a fast bowler.
Right after Bolt's triumph, Melaine Walker added to Jamaica's joy by taking gold in the women's 400 metres hurdles.
While her team mate Bolt and America's Phelps have given the standout individual performances so far in the Aug. 8-24 Games, it is team China whose overall record has dazzled the world.
The hosts, who came second to the United States in Athens 2004, have 45 gold medals, a seemingly unassailable lead that marks their emergence as an Olympics superpower.
That will delight the Communist government, for whom the $43 billion Games are a symbol of China's new global standing.
Local windsurfer Yin Jian pumped and glided her way to a first sailing gold for China. Then Wu Jingyu won gold in women's taekwondo on another successful day for the hosts.
The United States lie second with a less-than-expected 26 golds, while next Olympics hosts Britain are a surprising third with 16 golds, their best showing in a century.
Joy for Afghanistan
Global conflict zones like Iraq, Somalia, Afghanistan and the Palestinian territories struggled to send athletes to China, and some competitors had to prepare in appalling circumstances.
Swimmers have used under-size public pools, while runners have had to dodge bullets.
Against all odds, though, Rohullah Nikpai won the first Olympic medal in Afghanistan's history -- a taekwondo bronze.
'I'm very happy,' said Nikpai, who fell to his knees, hugged coaches and wept after beating world champion Juan Antonio Ramos.
Many Afghans were unaware of Nikpai's win because power is intermittent and few households have cable television.
The International Olympic Committee is delighted at unprecedented global interest in the Games.
It said online broadcasts and enormous viewership within China, the world's most populous country, had made the Beijing Olympics the most watched in history.
A record 1.2 billion people are thought to have seen the opening ceremony and 40 million people in the United States alone saw Phelps win his eighth gold medal, an 18-year high for the NBC network's Saturday evening viewing.
Trying to attract a younger audience, the Olympic movement is embracing the Internet and also allowing new telegenic sports.
In the first Olympic 10 km open water swim, Russia's Larisa Ilchenko won by less than two seconds from Britain's Keri-Anne Payne and Cassie Patten, sprinting past the pair in the last 100 metres of the jostling, rough-and-tumble contest.
South Africa amputee Natalie du Toit won admiration for her pluck in swimming the 10 km but there was no medal for the 24-year-old, who lost her left leg in a motorcycle accident in 2001. She finished 16th, around a minute behind Ilchenko.
As well as the water race, TV-friendly BMX biking got its first start, bringing some counter culture attitude and extreme sports buzz to the Summer Games.
To the sound of thumping music, bikers race down a three-storey start ramp, fly over rolling dirt bumps in helmets and protective padding, and crash their tiny bikes recklessly in action-packed races that last less than 40 seconds.
'Being a fast, intense spectator sport, it suits young people's expectations,' said France's Anne-Caroline Chausson, who crashed but made it into the semi-finals.
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